It's a fun game, but boy is it hard at the beginning.
It has great graphics and runs well, but that's what you should expect from Valve in the first place. It has it's on unique style of graphics that sets it apart from other games. The sound is also very nice, but there's not much to talk about in terms of sound other than the taunts and phrases the characters say.
Gameplay:
At the beginning, it's going to be extremely hard because the gameplay is very different from other games. You'll notice how compared to other games, enemies take quite a lot of damage to kill. The game gets fun after a while, but it takes a lot of getting used to. I'm still getting a lot of games where I get twice as many deaths as I get kills, but in this game it's not important at all. What's important is having fun.
Characters:
The most memorable part of this game. All of characters have distinct personalities and act stereotypically, but in a funny way. One problem I've noticed with the characters is that some of them are quite overpowered, especially the Pyro. I know the Pyro was made so that the Spy wouldn't be overpowered, but the Pyro does way too much damage. He's possible the only character that can kill a player in less than a second. I don't think anyone notices that. And to make matters worse, the Pyro runs pretty fast, so you have a slight chance of running away unless you're a Scout. That's the only problem I have with balance, everything else is great.
Overall:
Get this game and make sure you aren't VAC banned, or else you won't get your money's worth. If you are, then just make a new account.