I would recommend trying a few of the free trials out there and get a feel for some of the games.
I am currently a DDO player, which has a small player base and is a niche game, but the combat is more FPS style in a fantasy environment, dungeons are instanced and you don't have to travel from point A to point B over miles of virtual landscape. Instead many of the quests are a short journey after 'traveling' via airship or caravan or whatnot.
LotRO has a large player base (not WoW, mind you, but large). It is more WoW like as far as quest types and grind for xp, but it also has more entertaining fluff like guild housing and a solid crafting system, which DDO lacks.
EVE online was just relaunched, and while it has a steep learning curve and the community is generally very unfriendly towards newbs, if you can get yourself established it is fun.
If you are willing to wait a bit, there are some really good looking MMOs out on the Horizon. Cryptic Studios, the makers of the CoH and CoV have a new superhero MMO that is in closed beta atm called Champions.
And of course we have the Sci-Fi StarX MMOs all coming out in the next couple of years. Stargate Worlds is in beta atm, Cryptic Studios is also doing Star Trek which is still in Alpha and Bioware has Star Wars in the works.
Just some ideas for you. I would say try the DDO free trial, maybe fire up a new LotRO trial, or check out EVE for a new flavor.
