Okay...I have slept on it, and y'know, I'm okay with all the mod/perk/specialization malarkey.
Personally, I don't think they are going to alter the game all that much. I see people talking about how Halo 2 (pinnacle of the series my arse) was amazing because you could predict what an enemy was going to do etc. And yes, you could, but to a very small degree. You don't know if they have rockets, or shotgun or sword...usually until it's too late. Except now in Halo 4, they might have something and they think they have a clear cut advantage, but I may have a mod in my setup that may allow me to work a miracle and beat them in the encounter. Some of you may think that's a bad thing, I find that pretty interesting from a gameplay perspective. No more annoying than how I usually get beaten or beat someone. Just more varied, more nuanced.
For example, I love driving vehicles and supporting my team in BTB. So, the idea of a mod that allows me to regain vehicle health quicker is attractive. And one of my pals loves to gun, so he'd pick the mod that allows quicker turrent cooldown etc.
So we're cruising the battlefield destroying the enemy team. Now, we'd normally have to avoid the usual - stickies, rockets, EMP bursts....except this time, one of the enemy team might say to themselves, "I just got owned by that Hog, best use my anti-vehicle loadout" so they boot it up, and they might have a mod that extra damage to vehicles, or a tripmine or some other crazy thing. It feels like it's all about more emergent gameplay, tuning your spartan on the fly to counter different scenarios.
I know Halo is (or at least, was) an arena shooter, and I loved it back in the day. But as much as I may enjoy "classic" in Halo 4, I want to embrace the new and the different, because I'd rather play a game with lots of players, a game where wait-times are minimal, opponents are varied, gameplay is varied. I don't want Halo 4 to be the fragmented "try-to-please-every-tiny-subset-of-the-fanbase" that Reach ended up being, because that game became a chore to play. Have I got bloom this time? Or a little bit of bloom? Or none at all? Is there bleedthrough? Reach became a mess, and remains a mess.
Halo 4, for better or worse, is a very different game. The ability for it to be a stripped down arena shooter will still be there, but I plan to dive headfirst in all the new hotness and see how it plays out.
Hope that made some sense anyway.