Every MMO I've played, I start with a healer, get bored, and end up on a DPS type spec. I'll still play an alt healer character now and then, though, until I get bored again. I also have always started on a PvE server, then moved to a PvP server. I should really just always start on PvP servers from now on.. I will!
I also enjoy stealther classes, both because I can easily explore zones/skip agg and so I can sneak up on people and stab them a bunch of times A good ambush on a low defense yet high DPS/heals target can make a big difference.
As healer I tend to feel I'm not really in control, that the people actually choosing targets and zapping them are, and that I'm at the mercy of these other peoples' strategies, whether they want to try and rush in to a huge group or stick together (or keep breaking LOS ), etc.
That said, a good healer can make a huge difference, particularly in PVP, which is what I mostly enjoy in MMOs, although the more detailed quests (missions) of Star Wars: The Old Republic have kept me engrossed since the game came out.
Right now I'm enjoying the commando trooper on SWTOR, mostly DPS but with a little healing if necessary. I'm still enjoying SWTOR so I have a feeling I'll play every class to some degree, perhaps even all of them to 50.. When I find an MMO I like, I tend to spend a lot of time playing it, until I feel I've exhausted everything, and then I rarely or never play again (DAOC, WoW [it took 2 weeks ], RIFT).
Happy specs to you all