A while ago I discovered "Beyond Black Mesa" which is just an absolutely stunning fan film based in the Half-Life universe. Then a while ago, I found Singularity Collapse, which is also EXCELLENT beyond belief. I'm going to
The two are definitely different and I can't outright say which one is "better"; they're both very good. I'd have to say BBM is more like if they spun Half-Life off into a movie, whereas SC is more like the game itself: first person, interacting with people, not really knowing what's going on.
In any case, I'm still amazed by the amazing special effects and how they even worked in the a certain someone (you'll know who after watching). Give it a look, if you've played Half-Life, I sincerely don't think you'll be dissapointed.