feather240 said:
Halo was the first of it's kind so it's original, and I've yet to see a game copy HL2.
The original Half-Life practically introduced set pieces to single player FPS games. Before that, most FPSs were linear corridor shooters that didn't involve the player with his surroundings. Half Life added puzzles and made the environment a huge part of the gameplay, as large as the combat itself. Like Halo, it was the first game to do this, and many would follow.
As for Half Life 2, it's mostly the same thing, but with a splendid physics engine. It does the set piece driven/environmental puzzles thing so well though, that no one blames it for being more of the same. Not all games need to completely innovate and introduce wholly new concepts to be considered great games.