HalfLife2, real innovative gameplay? No. Innovative presentation, but not gameplay. HalfLife 2 basic gameplay is no different than the original Doom.
Actually, it uses the most advanced version of Systematic Level Design yet seen. It's design allows for creative problem solving: the player can actually invent ways to achieve goals in the game, using the interactive environment. See Harvey Smith's presentation about it at the GDC on Gamasutra for a better explaination of this type of game design.