I experienced some of this when playing through the same map more than once, with various difficulty and enemy density settings in effect. It was easy to tell that, while your group of friends might get used to the map layouts, the challenge you'll face will never be a known quantity. Over a series of a half-dozen matches, Zipper took my squad from facing off against a decent number of pretty smart adversaries to having our small group fending off an army of extremely well-armed, deadly accurate elite soldiers. The way this affected the pacing and depth of teamwork was clear as daylight; while we played the first couple of matches almost like a traditional shooter, we were inching along prone on the ground, spotting for one another and tightly coordinating by the time all was said and done.
I don't see SOCOM 4's co-op as revolutionary, but it's definitely poised to evolve this type of play in the genre -- not to mention serve as a strong compliment to traditional single- and multiplayer modes.
On the subject of the game as a whole, it's coming together in these final weeks before release. The level design, enemy AI, visuals and control basics seem fundamentally strong, save for minor, totally fixable bits like some extreme pickiness on character positioning for reviving fallen squadmates. The real test, though, will be the unpredictable human vs. human multiplayer where seemingly minor problems can balloon into game-breaking issues.
I would've liked to have tried co-op using a headset -- say Sony's own, now in camouflage! -- but the dev team didn't bring any along since it expected a more intimate, quieter venue than what it ended up with. Actually, I'd have traded that for the chance to swap out my one squadmate who didn't quite understand the concept of stealth. Eh, maybe he'd just gotten done playing a bunch of Bulletstorm.