I've had many of these and they are fantastic. The standard version came with the MC 90's up top, and a celestion V30 set in the bottom. The magic is the Halfback feature that is its namesake. You get the tight and percussive sound of the bottom enclosed with the open airiness of the open top. These are the best cabs Mesa ever made, IMHO. They look bad ass too. They have a smaller footprint that most 4x12's but weighed about the same, unless you ordered it with the optional EV's which were quite a bit heavier. Usually, the EV optioned cab came with the EV's in the top open half, while the bottom enclosed part still had the V30's. Those that got the high wattage EV option up top typically did so to get a loud and polished clean tone out of the cab. I have seen pics of all kinds of famous players using this cab back in the day, from Pete Townsend to Slash. The slant cab is seen more often than the bottom 4x12. The 2x12 slant is awesome as well. A pair of these on either side of the stage sounds huge! Wish they still made these. Some people had issues with the grill being prone to opjects puncturing speakers (i.e.drumsticks and the like). They are one of my favorite cabs. The only thing they have made that comes close to these is the Road Kind 3/4 4x12 cab, which has half of one side open, hence the 3/4 designation. It is also open vertically, not horizontally like the 'Halfback'.
The Halfback is definitely a keeper brother, and in a pinch, you can take the front grill off and cook up some steaks!