As for his current powers, it lets him swap between being like 7 different people, which in itself isn't all that amazing if it wasn't for the fact he can power up so much faster then everyone else.
For most people getting the power of what would be 10 levels would take years. he can do that in a few days.
Ofc all 7 of the classes have pretty insane powers....
Outside of the amazon who is useless trash and he only ever uses it like twice in the entire story unlike pretty much every other class who have at least one full arc to shine at full power.
The only reason it is good for anything is the surprise factor as everyone thinks bowman's are weak.
This is becouse after you hit "moon level" people starts being able to pluck arrows out of mid air and an army of weaklings got nothing on a single strong person.
His power can do more then just becoming a diablo 2 character ( a example of this is his ability to bring with him health potions outside of the "game world")
but pretty much all his extra powers are super big plot points so im not going to spoil that now