The WAD is good, but one HUGE problem in it is that some types of new monsters are fully invisible with their projectiles invisible too.
You're not loading skulltag_data.pk3 properly.
The only invisibility problem in RGA2 is hitting imp ghosts before their spawn state is completed.
@Voltlock: You should really use alot of the alterations from RGH, they further improved on this.
NR6 stands for New Release 6. It's newer, better and arguably less buggy than Hardcore which was based on the old release 11. (and doesn't include that godawful bloody screen)
I made a small addon for NR6 called Refined, currently on BestEver's wadlist. It's mostly changes and fixes like:
1,2 assault rifles instead of 2,4
smg's share slots with shotguns, OMA increases to 2
launchers share slot with lmg's and snipers
gun and ammo spawning less random
some balancing, including overall lmg nerf (including scar not being worthless and famas not owning m16a4)
Pain sounds work with skin, female sounds added
shotgun/dragon's breath fix for boss monsters
gldefs and fixed frame, sound and spritework (including doctored bolt pull action for the ump45)
Changelog's in the main wad. If you do ever return to RGA2, feel free to use if you'd like.