GTA I can understand. Halo, no.
It made little history in the FPS genre with its unique weapon system but other than that, most features hav already been done. It might have good graphics but every 3 months, a game comes out with better graphics so its hardly a game that made history aside from being popular.
I say. Half Life, Doom, Super Mario Brothers, GTA, Alone in the Dark, Street Fighter, Madden, Sim City and I cant think of any others. but there's more