I was lucky enough to get a look at this last week. It's a real fight all the way - and all the way is quite a long way. As has been said, the slopes (etc) are very well integrated into the map. It is a great tribute to 10 years of Doom, drawing on Doom looks and style but done in a modern way, employing tricks and features that simply weren't available in '93.
I don't know why that happened. Prior to release I ran through this map so many times that I lost count and it never crashed once on me. Very odd. Sorry if it caused you any inconvenience.
Thanks for the positive feedback guys, its appreciated