Something I've been watching for a number of years now (pretty much since HalfLife 2 was released I believe) is the "community" project BlackMesa (once called BlackMesaSource.)
When HL2 was originally released we were told we would have an updated version of HL1 remade in the source engine. Everyone was quite excited about this and those with more imagination than others forsaw a complete and total remake with new weapons models and textures and character models and...well, new everything!
Sadly this was not to be and Half Life: Source, as it became known, was pretty much a straight port to the new engine, the only major changes being the new water system used by the source engine, and some sky box updates. Sure there were other small changes but these were overshaddowed by the number of things that were still the same.
Luckily a small number of the "community" (I've never been sure that's the right word to describe a fanbase...ooh, fanbase thats a better word...) decided that they would actually do something about it and give their favourite game of all time the right treatment. I think everyone agreed that it was best to leave Valve to get on with future stuff, and thankfully they gave their blessing to the project (aparantely.)
And so Black Mesa Source was born! It first captured a lot of attention with some spectacular screenshots of a damn, which was a landmark location in Half Life. This particular screenshot has been used nearly anywhere this mod has been mentioned...except here because I'm too lazy to copy paste. But if you visit their site you'll see it for sure. Anyway, this has been in development for a long time because, like Valve, the developers want to get this right. After all it's a hard act to follow and there's a terrible monster of a fan base waiting to howl if it doesn't meet their (possibly unreasonable) expectations.
Personally I think there's a very high possibility that this will turn out to be a fantastic game, and from the looks of it will not only capture the spirit of the original game but will build on the experience and show us a different, more detailed and realistic vision of the Black Mesa Research Facility that wasn't possible back in 1998.
Anyway, here's a trailer they released earlier in the year which importantly states the Mod will be released this year. The cynical part of my brain says that's very unlikely, however according to their twitter updates they're still sounding confident about it. Here's hoping!