I saw Boyz II Men perform at the Terry Fator theatre at the Mirage and it was phenomenal! I have listened to Boyz II Men for almost twenty years so it was pretty exciting to find out they had a residency in Vegas.
The theatre itself was nice but the seats were a little small; felt cramped between the two people I was sitting next to (one of them being my 6'5" husband who sat awkwardly in the little theatre seat).
But it was easy to find, clean and great views from all over the theatre. If you have a chance, go see Boyz II Men when you're in Vegas. They put on an amazing show!