I mean listing Halo's relatively minor 'innovations' completely misses the point. The reason Bungie should be praised is because they curated one of the three-or-so FPS franchises left in existence (make that two if Far Cry 3 is another zombie CoD, as looks increasingly likely) that actually understand that the variability of experience (i.e. the permutations of interaction between the player, weapons, enemies, and level design) is more important than its presentation.
When everyone, the holy sainted Valve included (excepting Left 4 Dead, the other franchise that does this right) has gone the other direction, in pursuit of cinema, the scripted sequence, the linear path, the one-time, quick-time moment, it's hard not to adore Bungie for understand what's interesting about the interactive medium, and what's redundant.
That the majority of the gaming world doesn't even begin to grasp that, so consumed are they with petty grievances (that possibly have more to do with Microsoft and the Xbox than they do with Halo or Bungie) and the latest flash-bang corridor drivel, is simply depressing. It makes me depressed about the future of the genre, and even the entire medium.
Flawed as their execution has been (and it has been flawed, in myriad ways), Bungie grasp what's unique about videogames. So, so many 'authorities', even in this thread, don't.