Challenge and an emphasis on re-playability, powersets being distinct and unique in there own way. Even though CoH's blast/melee sets were "identical", they all had unique nuances and niche's that could change the strategy to how you played the character. Especially when combined with the defense, buff and cc sets, those nuances made for a unique experience for me. Especially as the semi-identical but not identical nature of the sets meant they were easy to figure out. They were different enough to make them feel unique without making them miss some fundamental core function.

I mean a kinetics/dark blast defender played very differently than a kinetics/energy blast or kinetics/fire blast. I know, same primary in those three examples but just changing the blast set, the secondary, changed fundamentally how the character would be played and how you'd IO them out accordingly. Or how dark melee could play differently than claws on any kind of scrapper. Or fiery assault vs say thorny assault ect. Just one powerset was enough, let alone changing both of them.

CoH was a game I'd get a minor case of altitus with it for just that reason, so many sets to choose from.

Edit: And course the community was diverse for me, then again I hanged out on virtue where the more mature players hanged out.