I've been looking into this map recently after noticing it being played at IEM 5, and I'm liking its balanced, defensive style.
Mega and red are at opposite ends of the map, and the map has the big three weapons (rocket, rail, and lg). A plus for a novice player like myself is that there aren't really any tricky jumps on the map (as opposed to bridge to rail on dm6). Having three major items as opposed to four makes a good challenge for the out-of-control player, and there are plenty of angles and choke points around the major items to work with.
Some downsides IMO include the presence of two rocket launchers on the map. Taking away one would make things more interesting and challenging. I like the rail angle on mega, where you aim at mega through a groundfloor doorway that's in between mega and red, but the mega area seems too tight to me. It makes rocket spamming a bit tedious at mega.
Overall though I like dism because it's a pretty cerebral, defensive map.
What are your thoughts on this map? Would you want to see it being included in mappools more often?