From the singleplayer perspective, a big update is the monster animations, the old cast comes much more alive with jumping and death animations, and all now independent. Fine new and added SP maps, one or two which use the new mapmodels, trigger switches and levers, which will be a boon. Not mentioned in the history is the collision works better for static mapmodels, improving its marginal floor-over floor capability. Subtle kickback on weapons adds a bit of feel, works well with SP since the monsters often get knocked back when they die.
Nits: may need to make cube/savegames folder yourself, map ramapge may not be able to find last monster, yadda: http://wouter.fov120.com/cube/forum.php4?action=display_thread&thread_id=313&start=231