If your unsure about Halo 4 than I'm right there with you. Just read the recent Game Informer for myself, and I think the campaign sounds fantastic and shouldn't disappoint, as it seems to be with all the Halo titles. However, like you, I am worried about the direction 343i is taking with Halo 4. Overall, Spartan Ops sounds cool as a short multiplayer side story, and I like how the missions will change every week, free of charge. I think the result will be more like MW2's Spec Ops gametype than the flop of Arena mode in Reach. Hopefully the multiplayer's integration into the campaign is not as heavy as it was in, say, Mass Effect 3 because if I want to play the campaign, I only want to play Campaign mode.
I will need a little more information to devise a proper opinion, but I think 343i really went mainstream with Halo in regards to custom loadouts and armor-specific effects (so now the armor permutations affect gameplay). Like other multiplayers, these two elements hinder a veteran's ability to weed out the noobs in a multiplayer that is built upon skill, not individual advantages. As for the loadouts, I doubt 343i will allow just any starting weapon, so BR fans will have their BR, DMR fans will have their DMR, and so on but nothing crazy. Please, no more mainstreamy elements. These advantages are what make me despise games like Call of Duty.
So, yay, no more armour lock. Best thing they took out of the new multiplayer. However, more Jet Pack? More Invisibility? Forerunner Vision? Just do what Halo 3 did - armor abilities collected and used in game by only those fortunate enough to run into them. Oh, and 343i made Sprint a universal ability, which I like. As for Firefight, it was fun when I played it, but I can't say I'll miss it.
So long as there is Grifball, I will be satisfied with the multiplayer