Playing through Ground Zeroes on PS3. Not really sure how to evaluate this game as I haven't gone through all the missions yet, but generally, this game is like Peace Walker with a sandbox level instead of having zones.
The biggest change in the gameplay comes from the new iDroid gadget which uses the marking-via-binos system. It's kinda annoying at first to use while trying to get used to not having the radar/sound detector, but with the sandbox level design and improved vision from the enemy (Hard mode enemies have almost realistic visual detection, being able to see from across the half the map if you're standing or crouching) it's probably the right thing to do with the new iDroid system.
From the two missions I've played so far which was the main op and a side op, I feel like the core gameplay is probably the best so far in the MG series. Kojima Productions have also made improvements to the gun combat(It's almost as fun to kill stuff as it is to sneak around) but personally, I think I'm gonna have way more fun wasting time trying to memorize enemy patterns and try to get the mission done without using any weapons including OP tranq. guns.
Oh yeah, one of the problems I have with this game is the bloody reflex(slo mo) mode before an enemy alerts the base. Since this game uses a score-based system which determines rank at the end of the mission, disabling it automatically gives you 7500 points(a lot) which makes me feel cheap for doing it when it's not supposed to.
And another thing is the checkpoint system, which absolutely fucks up the tranquilized enemies on Hard mode. For example, I got an alert far into the mission so I decided to restart from checkpoint. After restarting, all the enemies I had tranquilized earlier and had woken up had gone back to sleep again, with their sleep time probably at reset again. So you can see why I said I would enjoy this game at its most when playing without restarts and without weapons, hard as it may be...
Edit: Another one: Sound. When you're moving around, you make a shitton of sound even when moving slowly. If I remember correctly, previous games would have you make no sound when sneaking. That at least helped with immersion, but in this game, when crawling(the most silent gameplay-wise), there'll be all sorts of sound and the enemy casually strolling in front of you won't hear a damn thing. In fact, I must say this could be the most irritating thing about this game. They ought to tweak the volume for moving around.