If they were gonna get rid of Hayter, they should've gone with John Cygan (Solidus). Or hell, even Richard Doyle (Big Boss in MGS4).
The lines I've heard from Kiefer's performance have been absolutely terrible.
Well, what do you expect? Kiefer isn't a voice actor, and he's not much a film actor. He has a certain presence that is hard to deny, but that's mostly unconnected to his actual performance and their respective quality. SinceI just made a Die Hard thread in OT, I'll add that while Bruce Willis can carry certain films, he's not the greatest actor (he has some good work, much more than Kiefer), but you certainly wouldn't want him either as a voice actor. Same thing with someone like Harrison Ford. You can swoon because it is a person you've heard of, or you enjoyed their crappy TV show or acting roles 20 years ago, but for their vocal performances? No.
And, this may just be me out of the loop, but did people really complain about Hayter's work in MGS2 and MGS3? I only heard complaints about him in MGS4, and they just didn't like his gravelly take on Snake's rapid aging and throat/lung cancer or smoking effects after years and years of wetwork. I guess MGS3's voice work is too similar to MGS1 and MGS2, but did people think there was a nosedive in quality from MGS1 to MGS2?