Thanks for replying !
you have a point for the change of actor, (except that Big boss appeared three times(four?) with the voice of David hayter and that by MGS logic, Solid and Big Boss have the same voice/body) I didn't realy thought about that. Still not a fan of Jack Baer's voice, but I'm pretty sure that I'll just get used to it.

I do understand that the game as a lot of re-playability, but I'm still not sure why it's a separate game, I just can't see the reason why it's not TPP's prologue. The game is not a separate story. It just feels wrong to have the end credits after 50 minutes of game, additional missions or not.
I have to admit though that It makes me very interested in TPP, with a full game I'm pretty sure that GZ's concept can be awesome.
The game worth what I payed for it, but I just can't explain why it has been sold for 44$.

So, I remembered it right ? the whole "we are being investigated for nuclear threat" thing never appeared in Peace walker ? I haven't listened to the different tapes yet, the only one that I heard was very disturbing and added nothing to the game. Mother Base being destroyed was a pretty cool scene (I was hoping that the game with let me play that scene though). But again, It's a prologue, it's the only thing that happens during the game.

I do like the gameplay, I really think that it's a HUGE improvement over MGS4's changes. I talked about the gameplay only because along with the other changes it make me feel as if I wasn't playing a MGS game. The Roman number thing is pretty interesting !

As for your last point, as I said, the change of tone is VERY well done, It's one of the rare game that truelly made me feel a bit sick (and I've SO MUCH HYPE for Silent Hill now. Kojima proved to me today that he CAN disturb me and knows how guts and gore can make you feel sick without throwing buckets at the screen.) My problem with the tone is that it doesn't really work with the sort of silly stuff that MGS used to do... and is still doing. If Metal Gear completely abandoned the stupid shit I'd be a bit sad, but I'd understand why, it's necessary for the change of tone, they need to let that stuff go if they want to start talking about real stuff, real horror.
There is not a lot of "silly stuff" in GZ thankfully, there's a couple of things though, like Kojima breaking the fourth wall by jacking off while smilling at the player, really felt out of tone with the rest of the game.
But I've seen a lot of stupid shit in TPP's screenshoots (abducting horses and sheep with balloons for example) I'm fine with that if TPP goes for a lighter tone, otherwise I'm going to have a really hard time caring about the serious stuff the game will talk about.