Alrighty. I've been playing Halo since Halo 2, and I've considered myself a COD fan since COD2. I'm not going to say I'm a Halo vet by any stretch of the imagination, but I've played every one sans Wars and ODST since 2. Same for COD since COD2. COD has been my "go-to" game since 2.
That being said, Halo 4 plays NOTHING like current iterations of COD. Does it borrow some elements? Sure. Ordnance drops are very much in the COD spirit, and I can feasibly see the argument for sprinting. But that's essentially it. Halo focuses much more heavily on the ability to work as a team and control of the map. CoD's online is, essentially, a twitch shooter. Who shoots first, wins. Halo is more of a legitimate "fight" when a player engages another, and when a player loses, it's usually because they were outgunned, one way or another. Halo also lacks the CoD ability of a player to single handedly mow down an entire team, barring rockets or the incineration cannon. You HAVE to fight as a team, or you WILL die alone. Simple as that.
If the argument we're trying to make here is that the ability to have loadouts is too much like CoD, that's an evolution of the genre. Hell, Crysis 2 had loadouts. TF2 has the ability to change up your class (though not to the same extent). Halo isn't copying CoD so much as it is adapting to a mechanic that's popular. And it's not like it's an intentional move to alienate vets. Don't like loadouts? Slayer Pro says hello. I wouldn't be surprised to eventually see more Pro playlists added.
Halo, just as every other game must do, is changing. It's still Halo, it's going to remain Halo. As a COD fan, I WANT it to remain Halo. I like Halo. The alternative is it does what CoD has been doing since 4, in that it remains almost identical, and we moan about getting reserved the same game 4 (possibly 5...depends on how BO2 turns out) times over.
This is my two cents as a fan of both games. I like CoD, I like Halo, and I'm loving the hell out of Halo 4. I simply don't think you can make the logical jump that Halo's gameplay is "CoDified." It doesn't work.