I love MMO games and I pretty much play most of the beta's that appear. I am also a huge fan of loot collecting but also to social aspect of these games. It is not just about the gear, it is about the chance to play with like-minded friends and collect loot. :lol
Too Human has 5 classes that do play differently and have different abilities. Look at the spiders for instance. Add to this the huge amount of gear possibilities and also the great potential for expansive DLC. The downside is that despite all of this, 2 players just does not bring across the need to have multiple classes playing their roll to accomplish something.
As an example is the Defender class, who is the Tank class for Too Human. You have damage reduction skills, the ability to taunt the enemy, Spider that puts shields around you, freeze the enemy, all of this is classic MMO Tank abilities but they almost seem wasted by having 1 other person to use them on. Why give you all of these MMO style toys and then limit how many friends you can share it with?
I know SK said that 4 player would be far too hectic but let the gamers decide if it is too hectic. There is no story or cut-scenes, so it is really that difficult to add 2 more players? Just do it as an update for the Too Human fans.