TF2, 2

Pyro.
My favorite class in TFC. I have a tendency toward berserker rages or suicide attacks (this being one of the reasons for my name) so a shock trooper class is usually good for me. Still, I'm a bit disgruntled with the change to pyro in TF2 because it sort of pigeonholes you into that role. I liked the ability to harass or block off hallways by scaring people off with napalm rockets and napalm grenades. Adding more melee weapons also seems a bit pointless, since the flamethrower is a close-range weapon anyway and quite powerful in its own right.

Demoman.
My new favorite class. Combat in TF2 tends more towards close-quarters than in TFC, which means more enemies will be together to get hit by the same explosions. Delightful. The eyelander and other swords are quaint, but more of a trap for bad players. The main role of a demoman is demolition. All-melee players are bad players. When they do get kills it's by using their teammates as bait instead of actually helping to advance the team's goals.

Sniper.
Two things wreck snipers' odds in TF2. First off, most of the maps, as I said, are geared more towards short-range fights. Second, spies are ridiculous. They are overpowered and therefore overplayed, which means that by the time a sniper gets into position, there is probably already a spy waiting behind him. I do like the addition of the huntsman because staying on the move gives at least some chance of spotting a spy.

Medic.
Probably the most improved class in the game, mostly due to being able to heal at range. The variety of weapon and healing options, from overhealing to rapid healing to speedboosting to lifestealing are also very nice.

Spy.
The one glaring balance issue in the game. Only pyros can really afford to do constant spy checks. Everything else is food for spies. It's not just the invisibility or the one-hit kills. It's little tweaks like instantly disguising yourself when you get a kill or being able to endlessly disable/damage engineer buildings faster than they can repair them, or being able to 3-shot most classes even with the pistol. It's being an obvious counter to several classes while only one counters you. By the time I had played one half-hour match as a spy I had already beaten my score with every other class, some of which I had a dozen matches' worth of experience with.

Heavies, soldiers, scouts and engineers have not changed much in my view. The engineer's teleporter is very useful, but actually placing it is a sure-fire way to let a spy sap all your buildings to death. Then while you're trying to rebuild, he'll sap the teleporter too, after walking through it and backstabbing you.