I'm only level 28 tank spec, but so far, so fun. I have a 32 vanguard and the aoe on him is better than my guardian. I find my guardian more fun too play, though, which is just personal preference. I normally hate tank classes in mmo's, but both in this game are awsome imo.
I play on a pvp server, and while out questing on tatooine, a sith inquisitor, 4 levels higher than me, attempted to gank me. After he blew his load, my health was only half gone... my turn :-) force leap, blade storm, force push, force leap, stasis, force sweep, done, and I didn't even get to use my cd's. And Kira kicked the crap out of the sith's tank companion; still had half her health left.
I hope this isn't different at level 50.