If you like distinct visual armour upgrades then Diablo 3, borderlands 2 & firefall will leave you disappointed (same skins pretty much, different stats).
The skyrim & fallout series have great armour progression visually, but lack multi-player - most MMO's out today are pretty poor so that leaves them out of the picture also.
Firefall is a F2P FPS mmo, with skill trees & item upgrades (but no visual progression) - class based & pretty fun for a bash.
I'm also looking for a good co-op game with good character progression - so I feel your pain.