my primary concern is the “jack of all trades, master of none” problem. I’d hate for devs to feel like they have to develop for multiple tastes (and therefore water down their product - tacked on multiplayer is the worst offender here)
I can see the 3rd (2nd!) person perspective for tactical/cover based shooters (or portions of the game where this is the case) where ADS is less important, and the chaos of a firefight hasnt yet erupted. But for close quarters firefights it alters the gameplay component in a way i find problematic (I HATED the uc3 mp beta, and I loved UC2, and will likely love UC3 SP), and as mentioned, corner camping, etc. (one thing I felt was SUPER cheap about MGS4 was using the camera to see around corners my dude could no way see around)
for consistent gameplay and experience, sometimes not having a choice is better, b/c the devs can polish the mode they intended rather than trying to do everything (i for one, dont think its so simple as just flipping it on)