It's fun, replayable, you never go through the same strategies and power-ups, very centered around teamwork, mildly frustrating compared to its difficulty.
I don't like the limitation and weaknesses of certain classes and weapons, and the inability to remove powerups. Unless you have class X, you aren't going to win; if class Y doesn't have weapon A equipped, they're pissing in the wind; if class Z thinks about buying upgrade A, they're wasting money. Buy health on kill, more ammo, bigger clip sizes, more damage, faster reload on ONLY your primary weapon. Never upgrade your melee unless you're a Scout using the Sandman or Wrap Assassin. Demoknights, fat Scout, Sniper in general, Axetinguisher Pyro, Gunslinger Engineer aren't worth shit and will die quickly. If you start the game as this class, you have to stay that class, because you can't remove your $1500 worth of upgrades for the wave is too beefy for a Pyro.
But yeah. Lots of fun. Thought I bet you in a few weeks, I'll be back to almost 24/7 CP maps.