Well, let's see....
5 - Hideous Destructor - definitely the best mod I ever played, I really like realism in games and hideous destructor has quickly grown to be my favorite. It's pretty unforgiving at times, but it's still amazingly fun and satisfying to beat various maps with it.
4 - Guncaster - this one might be a bit bias, considering I'm a polish dragonlover, but I still highly enjoyed this mod and the fact that it can be played with heretic, hexen and strife made it even better. Plus hey, dergon power armor, so that's a bonus.
3 - Ashes 2063 - heck yeah post-apocalypse, although the weapons didn't feel that good to shoot, the amazing maps sure as hell made up for it, map04(?) reminded me so much of metro with going around a, well, metro filled with mutants. Loading the sterile version with hideous destructor is the closest I will ever get to my dream game.
1 - GMOTA - blasting demons with guns is good, but slashing demons with blades is even better. I really liked playing this one, it was fun doing combos with Blaz's sword and blaster, and you can always use a greatsword, which is a type of sword I favor the most, because everyone knows that big swords = best swords.
1 - Aracnocide - I'm scared of spiders so much, so when I heard about this one I just knew I had to give it a try. The weapons felt quite weak, but the monsters were just.... Too much for my poor heart, I was screaming my lungs out the moment I met the baron of hell replacements....
But that's just what I think.