I haven't played UC3 but all of UC2's puzzles are gimmicky.
They don't have "gimmicks" so to speak but they themselves are gimmicks in that they don't really feel natural-- they grind the pace of the game to a halt as you constantly look at your guidebook and push blocks around or climb on limbs of statues or whatever in a very sterile feeling room. They just seem like they're shoehorned in rather than part of the natural flow of the game.
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No problem!
This is a cute and pop genocide of love!