It has great game mechanics, but in all other manners of design it feels like a hodgepodge of unrelated assets thrown together. Quake 1 had a similar problem early in development, but they managed to tie it together. Quake 3 didn't even bother with a true singleplayer campaign, which seems like a winning move in hindsight, but at the time it was a departure from the norm and I can't help but feel like it was a move they did out of necessity.