Here are my thoughts about balance so far:
Overpowered:
-Spies. Cloak is 100% invisibility, not even a motion blur at close range, and lasts quite awhile. Their electronic sabotage kits do an immense amount of damage and you have to basically stand next to your deployables else you won’t get to them in time to remove the kit, PLUS it doesn’t kick them out of disguise. Their disguise is, to the best of my knowledge, impossible to detect without just shooting everyone on your team.
Underpowered:
-Pyros. They’re just awful. First up, you’re only slightly faster than the solider, but have 75 fewer hitpoints, and no way to increase your mobility via a rocket jump. Second, your flamethrower’s range is maybe three times that of melee. It’s tiny, and pretty much anyone except Heavies can out-backpedal you. The tooltip recommend they’re an “ambush” class, but the Spy is way, way better at that, since his backstab is an insta-kill. Most times as a Pyro you’ll pop out, start to burn someone, they’ll turn around and kill you, and then if you’re lucky, they burn to death. And don’t dare try approaching anything head-on, there’s so much knockback in this game and you’re so pathetically slow that you’ll never get in your puny range.
The flamethrower’s range needs to go up, and the Pyro needs a special power like all the other classes have. Maybe creating an oil slick on the ground that slows down people moving through it and ignites when lit? It’s more of a defensive role for an offense class, but then all the defense classes are amazingly strong offensively too. Would be nice to see one that turns the paradigm.
The sole use of Pyros I can think of is defending the intelligence in CTF, and hoping to ignite a low-HP Scout so he dies from burning as he tries to run. But intelligent turret positioning will do that fine.
Too important, ie, you have them or you lose:
-Engineers. Turrets are VERY powerful, and teleport pads can set up some crazy stuff. Dispensers are stationary, albeit slow, healers, and are good for stationary support classes like the Sniper. Without a turret network, you’re going to get steamrolled.
-Medics. Their healing is amazingly fast and invulnerability is just stupid and lasts forever. If your team isn’t using the Soldier/Medic or Heavy/Medic combo, and the opponent is, you will lose, simple as that. Fortunately they’re absolutely terrible by themselves, and thusly not overpowered.