So I just started playing Spiral Knights a few days ago, and here are my thoughts on it.

I started playing the game, I thought it was really cool, but it lacks some things, or some things could definitely be improved. First of all I found the recipe system to be quite odd. Only because of the energy cost to make things. It would be better if they reduced the energy costs in half, and slightly increased the crown cost.
Here is why:

I buy recipes, to make money off them by selling them to other players. But the problem is, that it costs 50 energy, and for now I am going to stay away from buying energy. There is no point of spending 50 energy on making a tier 2 item, when I would prefer to use that 50 energy to make more money grinding.
Don't get me wrong i'm not saying recipes are bad, but it would just make a lot more sense if there was more of a drive to use your well-earned recipes on actually making money off them. I know you can still make money off them, but instead of using that 50 energy to make 2000 crowns, you could start using that in the clockworks, and get yourself the same amount of crowns, heat levels, and various materials.

Im not ranting about the energy system though, because I like how you generally receive money faster in Spiral Knights, than in other MMO's , but you have a cooldown on how much you can play, unless you pay money or spend crowns, which I have no problem with (after all it's a free to play game)

In a lot of games I really don't like the grinding, but in SK I actually enjoy spamming right click on enemies for hours. I like the tier system as well, but one thing bothers me.

I really find it odd how large the gap between tier 2, and tier 3 is. Like the price of tier 3 items are usually around 4x the price of tier 2 items. Now I haven't gotten as far as to tier 2 levels yet, but unless you get a substantial increase in crowns, then the gap is too large.
I know that tier 3 items are more expensive, because the recipes are farther down, etc... but the stat difference does not equal the cost difference.

So those are mainly my concerns about Spiral Knights, but there are many more things I enjoy about this game. It has great potential, and I can see it getting better, and better as more content is rapidly added into the game.