I'll start with a link to an article ArenaNet published about a year ago: "A New Way of Looking at Healing and Death". This, probably more than anything else, was instrumental to capturing my interest (bearing in mind that when I first read this, I had never played Guild Wars). In particular, the second half, where designer Jon Peters explains why GW2 does not feature the dedicated healing and tanking classes of the traditional MMORPG trinity.
Now, let me preface this by saying that I played a healer for years in WoW, and loved it. During Burning Crusade, I decided to switch mains from my original rogue (created on release day) to my priest, and I never looked back. Peters gives an interesting description of the appeal of heals:
"It's not about clicking on a health bar and watching it go up, it's about being there for your friends when they need you"
That's what I was after. Having raided as a rogue for a couple of years, I yearned for a position of responsibility. I wanted to feel that I could make the difference between success and failure. Between the group wiping and me keeping them alive. Not between the group doing x dps and doing x+1000 dps.
Peters says "we don't like sitting around spamming 'looking for healer' to global chat". I'm sure dps players didn't like that. I didn't like having to call raids because I was there but no other healers were. I also didn't like it when I got benched because we had too many healers online that night! Granted, raiding was more flexible than 5-man instancing, where it really was "1 tank, 1 healer, 3 dps, or go home." But we still didn't have that much wiggle room.
The actual gameplay? The "clicking on a health bar and watching it go up"? That wasn't what I was there for. Don't get me wrong, playing reactively has an appeal over the pursuit of mechanical perfection involved in mastering your rotation as a rogue. But then I think about interrupting, as a rogue - a real high-pressure reactive role. Or playing a Guardian in LOTRO, where you have a raft of attacks that can only be performed following a successful block or parry. That sort of thing keeps you focused on the game, you don't need to be healing to be reactive.
Next thing on my mind: tanking and healing is a pretty weird implementation of heroic fantasy. I really can't think of tank and healer archetypes in the great works of fantasy. I felt far more like a fantasy hero playing Diablo 2 - slaughtering hordes of monsters before they could reach me and devour me, desperately running around to avoid Diablo's flames - than I did playing WoW, standing at the back of the group spamming heals. And if the trinity model doesn't really resemble classic fantasy, don't even get me started on Bioware's bizarre decision to try to bolt an EverQuest-style trinity class system onto Star Wars: The Old Republic. Yep, that's how I remember the Star Wars movies, lots of fights where an armoured rebel trooper stood in the front line, soaking up blaster fire, while a Jedi stood behind force-healing him. Ridiculous.
So, if Guild Wars 2 can deliver us fantasy action, where every player is trying to deal damage, whilst avoiding damage, interfering with the enemy via debuffs, interrupts and knockdowns, and performing a limited amount of healing, then I'll be ecstatic.