So I dled this game a couple days ago and decided to try it out. I have to say that so far I like it. I decided to make a warrior. Originally I played each class and stuck with warrior in the end cause it was just more fun for me. It reminds me of like WoW meets Maplestory meets Marvel vs Capcom or basically any other fighting game ( I know.. wtf right?

) but that's what makes it FUN. Doing combos and air combos. Muahaha. Lol.
I still don't understand things about the game like for the missions how do they decide your rank?
EDIT: Apparently US closed beta starts today.
For rank on mission, it depends on the stats on the right bottom corner. You want high damage, high combos (a big part of the MM for this game) and low...getting hurt (forgot the word they use). If you're in a party, at the end they add up everyone's combos, etc. To get 1 combo on a MM, you need a chain of 30. A chain of 60 counts as 3 combos, and if you get higher than that you get more too I think. Rank also depends on complete time. The faster you finish a mission, the higher your rank.
Up until recently, lvl 26 Hunter now, I pretty much got B/C on MMs. But now it's constant S rankings, A lowest. Things get a lot easier for better rankings after class change.
Good luck with warrior! I've had some friends reroll after the first class change. Classes at 2nd job change are pretty unbalanced, although they're working on fixing it since it's still open beta version right now. Jesters and BM should be nerfed, Gladiators and Knights and Assassins should be buffed. But I hear things change yet again at 3rd job change.
I haven't tried out the PvP yet though, that seems to be a lot more balanced for classes. And it seems fun!