The "house reef" at San Pedro has a gentle slope from the surface down to around 50', covered in green and brown soft corals. Then a very interesting formation of coral spurs separated by sandy grooves of varying depth and width down to maybe 120', with many overhangs, tunnels, swim-throughs, etc. I have never found such a formation anywhere else I have dived. Then down to maybe 180' a sandy slope with coral outcrops. then a gentle drop-off to a vertical wall that starts at around 220' and goes on down to at least 350'. Can't speak for anything below that!
It's received wisdom that the best diving in Belize is the walls at the atolls, and that this sort of diving is in any case diving nirvana. I don't agree, though I do expect to be in a minority of one. There's good wall diving all over the world and Belize's is OK, but the diving we have on the barrier reef is (almost) unique.