LewsTherin said:
The whole shield+health thing was a good idea, it's a shame they got rid of it.
EDIT

Got ninja'd on the health meter thing)They got rid of it in a way, but you still had health meter just not visible. The way I understand it is,(in halo 2-3 shield has X number of HP after it goes away the health portion starts depleting, after a few seconds the shield recharges but the health portion stays depleted only trickling up after a while. So while your shield bar might be full 100/100 your health might be 10/100 +5 every few seconds, something like that anyways.
Reason halo was innovative, mainstreamed FPS's on consoles, provided the best control scheme available (plus it was customizable every which way). Integrated vehicles in a manner not previously done so.
The two weapon limit made you think a bit tactically, no more I'll save this rocket launcher+sniper+shotgun+whatever, there was always a trade off. Shotgun+AR better not have long range encounters, sniper and pistol better hope there are no flood, Do I pick up the RL and lose the shotty? These kinds of choices it brought to the genre.
All weapons where useful, there was no pointless weapon, all had situations and strategies that each were best for. Granted the pistol in multiplayer was like having the right hand of God but at least everyone started with it(in slayer pro gametype)
It made Co-op gameplay fun, i'm sure many of us have enjoyed playing with friends/family on the same console. Plus Co-op goofing around was a blast.
It signaled the next generation of gaming on consoles, how many years where spent coming up with a halo killer? The graphics where great, it made great use of color, the environments where generally creative and diverse, USNC ship to beautiful Halo, to creepy jungle and instalation, alien ships, night on a desert mtn, snowy canyons. There was hardly two levels alike.
It set the standard recharging health mechanic(yet this one was actually realistic in the setting)
The multiplayer was incredibly accessible, balanced, yet deep. Newcomers could hop in and at least hold their own, while vets can always find a new tactic or strategy, there where many many gametypes from footraces, CTF, Slayers, King of the hill, oddball, and all of these where easily modifiable. (other games have had said gametypes but not all in one and not with the level of polish that Halo had)
It had a fluid melee system, I thought it was the coolest thing when I stunned an elite with a shotgun blast then proceeded to beat him upside the head with it. Or meleeing your vehicle and having it move roll or slide around.
Levels allowed you to go anywhere, barely any invisible walls around. Wanna jump onto that 30 ft high rock, throw a grenade and use the shockwave to throw you higher. Wanna perch on that rock 200 feet up a cliff wall? Go trek though the level and get a banshee. Want to get on top of the halo installations? warthog jump over grenades (Co-op) If you could see it you could reach it(mostly).
The level of freedom this game offered was unparalleled you where not shoehorned into a specific way to do an encounter, strategies where strictly up to the player.
Plus for me the story and the setting was amazing. When I first walked off that dropship and my eyes adjusted to the light, I was in awe there where waterfalls, trees a massive cliff that lead to an ocean, then I looked up and saw the halo itself with oceans and continents it loomed over you so majestically one couldn't help but just stand and look around.
Anyways that's why it was innovative to me.