This PC was from the beginning meant to be mainly DM maps for up to 32 players DeathMatch, as it progressed though it became mainly focused on SP and COOP. Some DM features are included but some maps are very poorly supported for this. Map01-04 should be the best though. There's some new monsters aswell as 7 all new weapons.
New levels from scratch
Deth, WadAuthor, Deepsea, BSP, Zennode, lvlinfo, Wintex, Deutex, need I go on?
Some. 1. Never try to save in map03. It will corrupt you savegame. 2. Doing a ingame netgame joining in map03 will cause the joinee to not see anything of value to him. His vision will get back to normal if you warp to map03 though(using the consol), or just exit the map.