From this weekend's beta
Note that neither thief or warrior were in my lineup before the beta. I tried them to see what I was missing, and to get a better understanding of all professions.
Warrior was more fun than I thought. The weapons provide a lot of diversity, and with weapon swap there is a lot of gameplay potential. I especially liked longbow + axes, though I can see liking another melee set with more experimentation. The hammer was pretty cool too, and so was the greatsword. Still, with ranger and guardian already making the lineup, warrior is not making the lineup due to too much overlap in gameplay.
Thief is as meh as I thought it would be, but I was disappointed about the initiative as it uses the same initiative across both weapon sets, therefore weapon swapping is not as useful as on other professions. I have never cared much for rogues either... I prefer the mesmer for confusing the enemy, and I prefer the ranger for squirmishing.
From the press beta:
Guardian is more tough than I thought, and the skills do require some good gameplay. Staff is not intuitive as a ranged weapon, but I did enjoy the scepter. I am still wishing for longbow.
I am liking the mesmer more than I thought I would. Casting and destroying illusions is a lot of fun, especially if you manage to confuse your opponent.
Engineer is fun, but complicated. I would like to be able to swap optional skill and toolbelt skill, in particular, it would be nice if kits were on the toolbelt because to switch to the grenade kit I need to press 7 instead of f2. Otherwise, it was a lot of fun.
Necro summons are more fun than I thought, less passive than most summons I know of.
I have yet to try the elementalist.