this is entirely subjective. whats better than halo. ask a halo fan what makes halo so good, and they will say it's halo. what an argument. why is halo so loved? because it has 4 player offline competitve, and was one of the first games that you could network. which made it's multiplayer extremely popular. popular doesn't always mean good.
HAZE was widely slammed for being a horrible shootertitle. certainly not perfect by any stretch, HAZE did things in an FPS(like stealing the weapon out of the enemy's hand after successful melee), that i had never seen before. and i had just as much fun playing it, as i did combat evolved(the only halo game i've played)
Killzone 1-3 are far more intense in thier presentation than halo ever was. and the characters feel substantial, not flighty. weapons react in a realistic way that even call of duty cant match, let alone halo.
resistance, probably the only true comparable game to halo, has a better main character(firepower alone, would defeat master chief with out much of a struggle), better story, more varied(and original weapons), and a superior enemy.
i honestly can't understand why the public at large fell in love with halo. it's not that great. it's a good game for sure, but completely undeserving of it's best ever status.
exclusive games better than halo(IMO):
FPS:
killzone 2-3
resistance 1-3
haze