I do not play in multiplayer (except perhaps Battlefield) and here are a few points to singleplayer:

• The game is too hard*
• The rewards for easier missions (Powerlever minus 50-100) are too low (100-300 experience points?!)
• Armor has misrepresentation (Assassin's head)
• Weapons have misrepresentation (pistol and sword at Crusader)
• Crafting takes way too long! At lower levels, it does not pay to wait an hour because you can get your equipment in a more convenient way.
• Customization options are too few or there are too few armor (my opinion)
• The assassin holds two-handed firearms in the direction of ground and hovers in part

* Why can not you make a game easy on Normal and harder if you choose a higher difficulty level? In Diablo 3 that is well solved. On Normal one is well rewarded and comes through well. If you want a bigger challenge you change the level of difficulty. At Martyr you can choose easier missions, but get nothing for it. (as already mentioned there are between 100-300 experience points ...)

Currently I do not have more points on the list. With me there were no real bugs ... it was just always too hard.

Thanks for the great game, love it! :P