One of the best multiplayer games of all time.
The graphics are great, now it isn't supposed to be realistic obviously, but they were clearly going for an almost, "Cartoony" look. They succeeded at this quite well, as nothing looks too fake, nor too real.
The gameplay is flawless in my opinion. Every class is played constantly by players. So they clearly must have balanced them well. Not many games make all the types of characters actually decent to play as. In the case of Team Fortress 2, they passed the expectations, and not one class is too powerful. The gameplay of each of the classes feel very different, some requiring more "Skill" than others, but all of them are playable. Every class balances the others much like a Checks and Balances system.
The replay value doesn't really refer to this game since it's multiplayer only, except for the recent addition of singleplayer with very, very, limited options. Even then, the game is addicting on multiplayer, just as any other modern game today is. Say, Call Of Duty.
The overall originality of the game is un-flawed, it includes humor and fun gameplay, you won't find another game like it. Upon the release of the game it really couldn't have been any better, so it deserves a 10. The game still gets occasional updates, so the game won't die out for a long, long, time.