I was in on the Tabula Rasa beta and it was FRICKIN AWESOME! I love it because, unlike traditional MMO's you control your character attacking. instead of press number one, then two, then three and wait for one to reset, it's more set like a third person shooter. you shoot a gun until its overheated, empty, jammed, or destroyed, then you switch to a sidearm or other secondary weapon, clear the jam, or run like bloody heck outa there! Its especially fun because there are whole fricking planets to travel too! literally, every PLANET has its own unique set of a dozen or so zones. Plus, you can move back and forth between servers, depending on how laggy it is! I didn't continue with that after the beta because i'm still playing LOTRO, which is the other thing I would recommend. LOTRO has a more traditional combat style of attack and regen, but there is such an in-depth plot line that getting bored would require (a not following the plot quest and just grinding against NPC's, (b playing non-stop for a couple weeks (my problem), (c there are two points in the game where you are too high level to fight the enemies in your area, and too low level to move on to the next. So that leaves you with either a loooooong walk to the North Downs, or nickel and diming it with lower level NPC's and quests. I currently am in the second of those two level barriers, but just getting out of it. Most of the reason I am still playing LOTRO though, is because i'm a "founder". A founder is one of the players who was in on the beta, and continued on into paying to play, and founders are given a special offer of 200$ for a never-ending account. basically, i'm in it for life.
So yeah, LOTRO or Tabula Rasa.
-Chupa