Weapons changeout. Fewer guns than the original 4th release. Consider it kind of a greatest hits collection. Also changed out some graphics, modified some attacks and threw in alternate deaths for the Shotgunner, Imp, Demon, Zombie and SS. And yes, they frickin' work. I've tested that up and down.
Scuba Steve Browning: Everything except for:
New from scratch / Modified (name of original file)
3 days (well, 72 man hours, worked by one man = 3 days)
Wintex 5.-something or other, Wordpad
Other than the usual EDGE glitches, not really, no. I'm quite surprised.