2.5D is fine as well but like I said I want to join the most active ones, is RO still active because I heard there's RO2 now and it's stealing it's thunder. I also hear Maple Story right now is the most active mmo right no in terms of 2D and 2.5D. Any other suggestions?
La Tale is quite active and in my opinion one of the better 2D MMOs and of course like people are suggesting RO of course, never was a huge fan of RO though (looking the same as everyone has always turned me off).
Oh you could also look into Starbound if you don't mind Beta, I'm enjoying that currently.