Coop wads in single player

At the start of last month I ran into DBZone on an ST coop server. Someone had applied GvH to it with mixed results, but I liked the map I saw so I decided to try it in SP with UV -fast. And it turned out to be among the best things I've played for ages - tactical, very hard in places with some interesting environmental challenges and health/ammo setups plus good looking maps to boot.

Has anyone else tried coop/invasion wads and found them interesting in single player? If so, what do you think the best ones are?

(I also tried the stock, alpha/delta and UTNT invasion wads last year, and only the big baron map proved too hard in 5 lives survival mode)

I'd love to do Invasion UAC by myself when I get the time.

Squadron 417 (and oldie) but it counts.

i like play coop doom tnt, i dont know why but i liked, and i like too play armageddon 2...