I don't think Halo is anywhere even close to CoD. To me CoD is like an arcade game, except you don't really have to even think. I just couldn't ever get into it, but to each their own!
Even with slayer there's substantial use of tactics (if you play as a team that is). BTB is a completely different game when you have vehicles, as opposed to when they're wrecking your team. In nearly any gametype using a pincer attack or flanking the enemy is typically pretty devestating.
As far as loadouts go, I feel it's mostly for playstyle customization. I feel like each has it's benefits and drawbacks, but none are clearly superior over the others. I use different loadouts depending on the map and gametype, and I feel they all have a use.
Ordinance isn't quite like the killstreaks either. You can get something decent that CAN help, but it's not 100%. You can get killed immediately and lose it, have it stolen,etc. CoD calls in AI to give you more free kills, last I checked there's nothing like that in halo.