Well you could move around with the Mark 2 on those briefings xD
What I was refering to is that whenever something awesome happend, the cutscene blended and made you play it afterwards like eg. bike scene, rex, rex vs ray, microwave, ocelot vs snake, ontop of derbins ride and so on. MGS3 only had the shagohod battle and Volgin was such a bad villain in my opinion.
I wouldn't call those "playing the cutscenes" at all. Only one that would possibly count was the bike scene against the Ravens, which was pretty much the Shagohod all over again. Nothing really new. What you pointed out were just fights or bosses that happened after they were introduced by long cutscenes that you were able to do nothing through.
The only instances where cutscenes were playable was the mission briefings. Even then you don't really control the characters. The game simply gave you something to do (like finding another battery, and looking at different angles of the area from a little robot) while the actual cutscene took place (and forever, at that) and you had no way to influence it what so ever.
What I meant was more: You watch Snake on a bike. You play Snake on a bike. You watch Snake control rex, you get to control rex. Snake jumps on Drebins vehicle, you get to be ontop of it. Snake and ocelot fight -- you get to fight. Snake enters a microwave chamber, you steer him. Snake holds off the gekkos while Raiden and Vamp fight in a splitscreen similar cutscene. There were so many epic shit like the ones mentioned above and all of that was lacking in MGS3. I expected to be wow'd in the wrong way basically.
So in other words, you watch a long-winded cutscene and play the game right where the cutscene left off. I wouldn't exactly call that blending in or playing the cutscene; hell, every other game does this. The only games, apart from RPGs, that I would consider the player playing the 'scenes' are Uncharted 2 & 3 since it seemlessly transcends from gameplay to cutscene (and vice versa) at various times. Take the bar fight in U3 for example. You throw a couple of punches, then a short scene occurs, and then you're playing it again without even noticing. I admit; I didn't know for a few times if it was a cutscene or actual gameplay. That's one of the few things I liked about U3.
The only scene in MGS4 that I would consider the player "playing the cutscene" is the microwave scene. The mission briefings, to me, felt more like having a different camera angle, and you couldn't always control Mark in the mission briefings.