Because everyone is on the edge of their seat dying to hear my opinion, here's what I think of each class.
Ranger: Probably the best class for new players. Fun and easy right off the bat. Just avoid the longbow because it's dumb.
Elementalist: Overpowered, your dps is so high that nothing has a chance to kill you. Whatever weapon you choose to use, fire burns hard. Air is pretty cool, water and earth could use some work.
Warrior: The underdeveloped class. I like my warrior, but it isn't as fun or as powerful as everything else. You need too much toughness to be viable in dungeons.
Engineer: A great class for new players and veterans alike. It seems that ANet put a lot of TLC into them because they are so well-rounded and the overall engineer experience is varied and interesting.
Guardian: Fun to play and you never die. Oddly you start with a mace and shield and that turns out to be the LEAST interesting weapon choice for the class.
Mesmer: delayed gratification. A powerful, fun, and well rounded class, but only to those willing to wait for the reward. For the first 50 or so levels it can be a bit hard to really see the beauty of playing a mesmer.
Necromancer: It's a fun class, but doesn't really feel like a necromancer. Instead of running with zombies and skeletons made by controlling felled foes, you just run around with a bunch of ugly pets.
Thief: a bit like the mesmer in the sense that it takes a while to see how they can be fun. The difference though is not that you have to level past 50 to really work right, but that you have to experiment with a gazillion diferent weapon combinations.
Any comments/opinions? I actually do like hearing others' opinions.