So far, reviews are pretty split. Examiner gave it a 1/5 in their review and also had an article up explaining why this is a scam. Curiously, both articles were taken down.
Famitsu gave it 38/40 which is less than the perfect score they gave MGS3 and 4.
Gamekyo have it a 4/10. Apparently, they beat the main story in 25 minutes rushing through. I've heard a few other accounts saying similar. There are 4(?) side missions (and they boil down to fedex missions) which extends this to 1:30 hrs. All these missions take place on Camp Omega (which we've all seen a ton of already). I've read one account of someone being able to do an 18 minute speed run.
A lot of people are also talking about how this is some of the most convoluted MGS story aspects they've ever encountered, but I've always liked that about MGS.
Most also agree that this is basically a glorified demo that should not be a $30 game. Even $10 is apparently pushing it, because its the same length as the MGS2 demo (and leaves off on a really bs cliffhanger apparently).
Also disappointing is how much they nerfed the mechanics:
Before you start piecing together its detailed systems, you'll notice that the basic mechanics and design have been minimized since MGS4, a decision that's sure to be divisive. You no longer have a camouflage percent dictating how hidden you are, so you'll have to rely on trial and error to gauge the effect things like darkness and shrubbery have on your concealment. Snake also doesn't have a "stamina" or "psyche" meter this time around, nor does he have a radar. Instead, players must zoom in with binoculars to "tag" enemies, making their movements visible even behind walls.
The good news is that it takes work to unlock the console exclusive missions meaning you'll have to do a lot of searching and hunting. That will add some replayability. The entire game has a ton of tactical elements bring a great amount of replayability to the entire experience too.
In a lot of ways, there's really a lot to Ground Zeroes. Its small scale is more than compensated for by its robust depth, but its conclusion is anticlimactic, despite its bombastic and lengthy denouement cutscene being exciting in and of itself. Indeed the biggest issue with Ground Zeroes isn't its length: it's a lack of closure.So Ground Zeroes is hardly essential, but it accomplishes what it set out to do in giving players a taste of how a more open-ended Metal Gear adventure might feel. Its wealth of strategies and secrets unearth plenty of tactical treasure for those willing to dig - something the premium price deviously encourages. Those expecting a full game are going to be disappointed, however - Ground Zeroes does feel like a very expensive demo. But it's also a very, very good one.