Something Missing
I've been playing for awhile, but right now I don't feel like there's anything keeping me interested in the game anymore.
There's no deeper story compelling me to keep moving forward and dungeon crawling. There aren't any real boss battles to go do with friends, or rare drops that I want. Recipes started out as fun, but when you're consistently missing that one last rare drop you need, the grinding starts to feel useless. There's no auction house or market place, so you can't even buy/trade for the item you need. Unless you shout in the arcade and hope someone has the item and are willing to trade you for it.
There's not even any joy in grinding. I've played Wow and Ragnarok Online, and I don't mind grinding for items. In those games if I grind and don't find my item, I can at least feel good that I got more experience or a new level or discovered a new area. The problem with Spiral Knights is if you go out looking for items for recipes and you don't find what you're looking for it feels like a waste of time. Yes, you can get some money and drops, but most of it is useless (At one point I had over 100 red, blue and green shards each. What the crap am I supposed to do with those?! They're barely even worth selling at a whopping 1 crown a piece!)
I guess the main problem for me right now is that there aren't enough little "highs" to keep me interested in the game. There's no feeling of success when I reach a new level. There's no striving to learn a new skill or spell. There's no excitement when I get a new weapon, because I only got that weapon for a recipe and I'm trying to level it. The good armor/weapons are too expensive, and the lower level items feel like a waste of crowns. The customization options feel limited (I want cuter items! I want to be so pink and cute that you will puke rainbows when you see my character)
Anyway, tl;dr:
SUGGESTIONS:
- Make drops worth more.
Give the user the choice of either saving up and buying a good item or waiting it out and getting a recipe. Having shards drop like rain but having the price so small makes them feel worthless to pick up, rather than exciting. - More customized items (with preview)
Have some low end items that make your character look cool, but might not be the best statistically. Also let the user decide if they want to switch their color palette, they can at any time. Also: cuter items - More mid-bosses
Give people a reason to group and take down a boss. - More Puzzles
I noticed that there were some small puzzle solving in some levels to open gates. I liked those! It switches things up and helps make it interesting - Increased skill set
You don't have to make 'classes' but having a wider range of options would be nice. I have heard some people complaining about wanting to have a healing/medic skill, or at least being able to cast spells to change up the attack - Reputation
Just an idea, but a reputation, where you can "like" or "dislike" a character so people can tell what type of person they're partying with. I have the feeling that the more people that come on, the more you're going to want this. - Number of times in a gate
Sometimes I forget how many times, or if I've even been through a gate. Some little number indicator would be nice - Auction House or Player run Stores
Give players the needs to find what they need, instead of shouting and running around the arcade
I would like a in-game bestiary though, just a simple version of what wiki has that has a pic of the mob and drops you have gotten from it.
This has almost certainly been suggested elsewhere, but I'd like to see an NPC trading post for items. A bunch of shards gets you a level two item. A bunch of level two items gets you a level three item, and so on.
That way runs that don't drop that item you want are still productive, and running difficult levels is more productive than running easy ones.
I think I heard that they want to implement an auction house, which is much needed and is essentially the same thing.

Good ideas, but reputation always ends up in failure leading to its removal.
I'm new here, but already saw that this game have a lot of potential. A lot of puzzle and mid bosses in repeatable group only dungeons, larger groups, a lot of skills and customizable equip, to make characters more unique, and a auction house/npc intermediary for sales would make the game really good, and would improve it's playabillity a lot too. About a storyline, they could begin to think about one, with dungeons/levels with temathics involving the world of the game itself
While I think expanding the skill set too greatly would kind of defeat the purpose of the game, some healing abilities would be cool. Maybe a staff that can go in an extra weapons slot that heals players on contact or a TF2-esque medigun, perhaps?

Great discussion so far, keep it up!
I will add that I am personally not inclined to ever add a player skill/weapon/anything that can reliably and repeatably heal another player. The game was designed to never need a 'healer class.' However there is plenty more we can do with other forms of player to player support and we plan on exploring some of those things in the future.
If no healing abilities, then can you make it possible to give health units to other players? The way health distribution is set up makes it incredibly unbalanced when somebody joins in the middle of a run with 5 units when everyone else has 10. Plus, in the heat of the action, you often accidentally grab a health unit you don't need and wish another party member would have picked up.
Something that I'd like to see if you are not going to have a healer is a "tanker".
I don't mean in the normal sense. I mean someone who has a zone-of-control, a way to keep monsters from passing by in narrow passages. Maybe this can be overloaded, but under normal circumstances, say, the first three monsters attacking get engaged, and cannot go past.
Now, such person will take a lot of damage, and so would get the health bars, good armor, etc. But it lets the gun shooters in the rear work just fine.
This is less useful in open areas -- monsters can go around the ZOC. And, smarter monsters will stay outside the ZOC until it gets overloaded with the minions to keep the tanker busy. Then, they go past the busy armor shell to the tasty stuff behind :-)
Note what this doesn't have. It doesn't have a concept of agro or agro management. It doesn't have monster taunting to draw their attentions. The monsters cannot go past, because this person has skill at engaging in tight areas.
Or just use weapons with good knockback and stun to fill the role of crowd control, since that's more what you're describing than tanking.

Broseph - We are currently discussing a new way of handling vitapods that would achieve what you're describing. It's on the list.
Curtai - What you're describing sounds like players basically forming walls, utilizing dead space as a defense, I like it. I've got something on the design wiki that also achieves what you're describing, however my interpretation involves cooperation between two players. That said, I can't go into details as I try not to talk about design concepts as if they are a current feature. Once we get closer to that point (implementation) you will begin hearing more about it.
It comes from my days playing hex-grid wargames. Units typically had zones of controls affecting the hexes adjacent to where they were.
The behavior varied on the game, and the scale (individual units versus squads or divisions), and what the game was about, but generally it either slowed you down, or stopped the rest of your turn, when you entered (or in some cases, left) a hex adjacent to an enemy. One individual-level game had the mechanic that you were stopped unless there was another allied unit in that hex already -- so you could send a few people in to keep someone busy, and then move through to overrun.
Alright, we're actually close to this now, apparently. You can shoot through a friendly shielded unit.
So, here's a specific suggestion:
1. A unit with either a gun or bomb ready, and no shield up, has no zone of control. Enemies can move past you.
2. A unit with a sword out, and no shield up, has a zone of control large enough to block a "narrow" passage. Small monsters can move past at the edges, but normal and large monsters cannot. In large open areas monsters can move around you.
Q: If you are in the middle of the passage, do you block completely? If you are at the edge, is that where you let smalls through on the other side? Does left-side or right-side matter (do you swing and block on the right and forward, letting the left side open?)
3. A unit with a shield up has a smaller zone of control. It will partially block a passage way by itself.
4. Two units with shields up, or a pair with one sword and one shield, will completely block a passage way.
The server will simply treat this as a "wall" to the appropriate creatures.
Result:
1. A single player can actively protect backrow shooters at the risk of using swords, and taking damage. Or, slight protection if shielding.
2. Two people can completely protect backrow shooters, but get "bounced" back when hit -- this will require the party to alternate front row shielders and backrow shooters.
What's considered a large, medium, or small monster? So far, I think some small devils would count as small creatures, and the tree-like constructs as large. Slimes and jellies? Probably small. Wolves? Medium, but they'll want to stop and attack the first creature, rather than going past to the backrow. Tongue lashers? Small, but prefer the first creature also?
No new classes, or skills.
Just the effect of using a sword, or multiple shields in a small area.
Most of those suggestions are alright, but please, no rep system. The players with the highest rep are the ones who go around spamming, "rep4rep," and you also end up with players who threaten to lower your rep if you don't give them what they want. It's just a system that has no effect but is waiting to be exploited. It serves no purpose other than to allow players to prejudge each other.
I also don't see much point in showing how many times you've played a gate, but I can't think of any reasons against it, either.
For the increased skill set idea, maybe this could be made into some kind of perk system?