It's a shame, really. I for one am NOT ripping on halo. I'm just pointing out the obvious.
What halo did, what the others did not do before are two things. One has been mentioned already, the recharging shield thingy. (and this one is something they deserve some credit for; in a non-tactical shooter it really gives the gameplay what it needs.)
The other one was microsoft backup. Microsoft used halo to market the first xbox and it was a HUGE worldwide campaign, pretty much the biggest when it comes to videogame advertising. I kid you not, look at the numbers. In fact I'm 95% sure, up to that point NOBODY ever used more money and effort to market a videogame or the according console.
If there's something topping those numbers, it's the later halo parts, and that's it.
And it would be a shame really to acknowledge THAT. The game and the meat of it, is, like I mentioned, mediocre to decent at best. It's okay, it's a fun shooter, but it was hardly innovative or great or anything. Just because you didnt play the shooters that pulled the halo elements properly before halo did, doesnt mean they dont exist
edit: just fyi, I grabbed a job at the local xbox presentation back in 2000something so I could be one of the first people in europe to play halo.
I was very interested to see what it was all about. I was very dissapointed to see, yet again, how easily people are sucked into the hype.
And
this is all what's left now.