Right have played a couple of them and I must say there is no excuse for not giving these a try as they are free.
I quite liked Spiral Knights spend a good 4 hours on it and it is a game you can sit back relax and play. Not much thinking needed just run around as your little character click and press a couple of keys and progress your way through.
Controls and graphics are very simple however the content was a little confusing for me.
I am the kind of gamer that jumps straight in... Instructions are for women
and there was quite a bit that I didn't understand in the game.
Also played Champions Online and I was not a fan. Can't give you much of a review because I had turned if off within 10 minutes.