This is just some stuff that's been on my mind, so I'm just gonna spew it out. Do forgive me if I ramble a bit. I'll list topics as I think of them.

-----First Batch (Friday evening)-----

Friendly Mecha Knights
-Friendly knights will try to block player projectiles, but not monster projectiles. Fix, please.

Rescue/Ally Knights
-See the previous comment on blocking projectiles, since they use the same behavior.
-Adjust the AI to flee from Grimalkins. While I find it hillarious to watch the idiots chase down the invincible monster (and useful that they're taking the chomp for me), it doesn't really make in-setting sense.
-Speaking of Grimalkins, I've noticed that rescue knights don't get back up after being KOed by Grimalkins. They just kinda sit there. Moping.
-I would love to see different "styles" of allied knights, probably based off the guys you meet in the Hall of Heroes, complete with different weapons, attack styles, and defense styles ("heavy" knights will block projectiles, "light" knights will dodge).

"Objective"-style Missions
-(So far, the only mission of this style is "rescue the captured knights", "reach the camp", or "activate a terminal".) When the mission has an objective other than "reach the exit", it should be possible to reach the exit, but fail the objective. Hide those objectives in a side-path, force us to explore a bit. It's kind of insulting when you just give it to us, and block off other paths until we take it. I mean, I don't want to fail, but there's no accomplishment to it if I can't fail.

Candlestick Keep
-Fix allied knight behavior around Grimalkins (mentioned earlier).
-Please do something about the Grimalkin spawn rate and spawn cap in a multiplayer game, preferably scaling it to the number of players. My friend and I have been facing a lot of the suckers for just the two of us.
-I'd like to see a general buff to candle range and duration, but that may just be me. That, or just quit forcing us to fight outside the range of candles.

Devilish Drudgery
-Woo, this one is a doozy. Pit Bosses are fine challenges when you throw them at us in regular rooms with a regular number of mobs, but many of the battle rooms in these levels have several groups of mobs to fight at once, AND these rooms are filled with traps. That, combined with the already frustrating behavior of Devilites (I'll touch on that one later) makes these levels far more dangerous than any of the other family-specific zones. Please reconsider the construction of these rooms.

Supply Depot
-As much as I like the concept of buying advanced gear with Energy, those prices are outright insulting. 30/100/300/1000 might be reasonable.

Forums
-BBCode is your friend. ;)

Devilites
-Devilites are the only monster whose attack is primarily ranged who also dodges player ranged attacks. One or the other is cool, but not both. If they use ranged, let us use ranged. If they dodge ranged, make them come into melee.

Battlepods
-These fights were cool at first, but now they're just tedious. Sit outside of range, swat down generator monsters, wait for shield to drop, get in a couple hits, fall back to outside of range. Rinse, repeat. I recommend two things:
++Gun Puppy style "turret" as part of the pod. I shouldn't be able to just sit in one place outside its AoE range.
++Breakable shields standard. There was a Battlepod in one of the missions that, instead of a full shield that went down after a timer, had a rotating shield with breakable segments. I enjoyed that battle a lot more, because my ability to damage it was based off my efforts, not some arbitrary timer. I was doing something, rather than just waiting.

Beast Healing Mob?
-Undead have a turret. Fiends have a healer. Constructs have a turret. Gremlins have a healer. Slimes have a turret. Beasts have... Nothing? Complete the pattern!

Side-Missions
-I'd like to see set-difficulty non-rotating missions that weren't required for rank. You know, side-quests. Expansion missions that you didn't have to buy. (Or that you buy with in-game currency.)

More Bosses, please!
-Like, 2 more T1 bosses, one more T2 boss, and one more T3 boss, and you'd have a full set. Only half would be in rotation at any given time.

Antigua lines
-Since you moved the Antigua upgrades to pure Elemental or Shadow damage, please introduce a line that is pure Piercing damage.

-----Edit 1 (later that night)-----

Shields
-When dealing with constant damage - mainly from traps, but also from a few monster effects like Battlepod gas or Chromalisk spit - a Knight's shield shouldn't ping down as absurdly fast as it does. As it stands now, the damage will ping your shield several times per second, shattering it extremely fast, and the flinch from each ping will trap you in it until the break happens. If your shield takes damage from a constant effect, there should be a second or two before it takes damage from the same effect again.
-If the wiki is to believed, the Defense and Status Resist properties of a shield only apply to the health of the shield. This isn't clear in-game; please fix.

Lockdown
-In the scoreboard at the end of a match, there should be fields for "distance dashed", "damage healed", and "death marks". Damage isn't everything.
-Please find a better way to balance the teams in random matches. Easiest way would be by total equipped stars, although that could still be exploitable.

Ironclaw Munitions Factory
-The rockets and shock traps in this level cause some serious lag on slower computers. Please find a fix, maybe by quietly turning them on/off depending on where the players are.

"Heat Share Slot"
-A new type of unlockable equipment slot, more akin to a heat booster. Any equipment placed in this slot doesn't provide any benefit to the knight, but gains a full share of heat a the end of a level.

Sleep
-Either bring it back, or get rid of it all the way. Don't keep it in limbo like this.
-Also, unless your bring Sleep back all the way, adjust armors that give Sleep resist to do something else.

Weapons preview/binding
-Please give us a way to preview how a weapon plays before we bind it. Maybe if equipment didn't bind if equipped in the Training Hall (and unequipped when you leave).

Bombs
-Bombs with lasting effects (mainly Vaporizers) are really spammable, particularly in Lockdown. Maybe if you can't start charging the next bomb until the current one is done.
-That said, bombs kind of need a damage buff to justify the time investment required to place one.

-----Edit 2 (Saturday afternoon)-----

Trojans
-I'm tired of being trapped in corners by these guys. Please make them vulnerable to shield-bump.

-----Edit 3 (Saturday night)-----

Monster Healing
-Any monster that can provide healing to other monsters should not be a valid target for healing. I'm looking at you, Gremlin Mender.

-----Edit 4 (Sunday night, week later)

Devilites
-Again, I plead. Please nerf. No other monster type thrashes me this reliably. Yes, I'm wearing shadow armor. Yes, I'm dealing piercing damage. Their projectile moves faster and charges shorter than any other. Pit Bosses turn their damage from moderate to deadly. Please. Please please please. Do something.

Silvermail
-There is no corresponding helmet that gives Piercing/Shadow resist. Oversight? Similarly...

Divine Mantle/Veil
-...Kind of a pain in the arse that Elemental/Shadow resist is only found at 5-star. Would be great if this split off from the rest of the Magic set earlier.

Blast Network
-Bombs and their blasts "snap" to the grid. Why don't players? It's not cool that I can have barely a toe in the line of fire, look like I'm safe, then die.
-In the same vein, it's not cool that I can somehow be trapped between to adjacent bombs. But having players exist only in one square or the other would fix this as well.

Arenas & Mecha Knights
-More a question than a suggestion, but why do Mecha Knight hordes appear in every type of arena? I mean, I'm cool with creatures from other families appearing in arenas, but there are always Mecha Knights. I guess I'm just asking for a bit more variety in the non-theme monsters.

Bombs
-I'd love to see a piercing equivalant to the haze bombs and Dark judgement. Maybe it leaves a field of spikes behind.
-I'd also love some kind of bomb that was thrown. It's always bothered me how reactive bombers have to be.

Aaaand that's all I've got. I'll add more when I think of more.