Mods I have downloaded and enjoyed:
Half-Life 1:
Mistake : Horror mod in an asylum. Only 20 minutes but I thought it was fun
https://www.moddb.com/mods/mistake
Mistake-1 : Prequal to Mistake. Much longer and better.
https://www.moddb.com/mods/mistake-1
Afraid of Monsters : I’m still stuck in the hospital, but it’s been fun so far
https://www.moddb.com/mods/afraid-of-monsters-dc
They Hunger : Again, haven’t really gotten anywhere but so far it’s had an interesting horror theme with a church.
https://www.moddb.com/mods/they-hunger
Paranoia : Keeps crashing, but the textures are nice and the weapons and cool.
https://www.moddb.com/mods/paranoia
The Trap 1.1 : Puzzle game I find enjoyable
https://www.moddb.com/mods/the-trap
Decay : Good if you can beat it
https://www.moddb.com/mods/half-life-decay
Half-Life 2:
Dreamball v1.2 : Like marble blast. Sadly, not many levels.
https://www.moddb.com/mods/dreamball
FLIPSIDE : Very impressive. I’m not sure how you make this with the source engine
https://www.moddb.com/mods/flipside
Get a Life : The story doesn’t seem to be developing well, but it opened up well and the weapons are cool. Somewhat horror, most just lots of zombie shooting though.
https://www.moddb.com/mods/get-a-life
Dear Esther : I’m not really sure what the point was, but great voice acting and music. Almost poetic.
Portal:
Portal: Prelude : No voice acting, all computer synthesized, but good storyline and much harder than normal portal.
https://www.moddb.com/mods/portal-prelude
Portal Flash Map Pack : No real storyline, but interesting boss fight and again, a lot of very difficult portal maps
https://portalmaps.wecreatestuff.com/
Unreleased:
Mentality : It’s for Half-Life 2. Zombie horror shooter, the beta was fun to play.
https://www.moddb.com/mods/mentality