The Source engine is a 3D game engine developed by Valve Corporation. Its unique features include a large degree of modularity and flexibility, an artist-driven, shader-based renderer, accurate lip sync and facial expression technology, and a powerful, efficient and completely network-enabled physics system.
one of the best engines that i have EVER seen... It seens that this is recent but actually its from 2002-2004... It has been developed along with half-life 2 (interesting fact is that hl2 started its development back in 1999, but by that time valve was still using the goldsrc engine)
Now its beginning to get older, and after using tools for engines of the past 3-2 years, it does begin to show up Source.
It is still a great engine, it works on many set-up's, it does not take much at all to get a map started, and with some basic logic, and the modelling/importing process is not at all difficult, however quite lengthy for today.
Writing out QC's and ensuring it is correct is sometimes a pain. Although basic models are quite easy, whereas certain commands and tasks can be a tricky, and touchy, fixing it can sometimes be something very minor, which can be overlooked when you have a complex QC, especially for characters and vehicles.
Compling maps, in the way Source does, is very old and patience is needed if your not used to it. Models not so bad, but for most engines these days its a one click export, and material files are made on the spot with little manual work aftewrwards. Its purely speed and convenience.
Well documented, everything you need to begin with and learn is in the Valve Docs.
Great games can still be produced and mods, but every year it gets older and even despite the updates valve provide it, other areas are still far behind.
Despite it's age, the source Engine is an ever-expanding, fully functional game engine with many perks and capabilities that I feel make it an excellent choice for Game Developers and Modders. While it lacks some of the qualities that other Engines posses (such as DX10+ Support and Large-Scale worlds), Valve's continued efforts to expand upon the Engine to insure that it remains compatible and glitch-free are certainly one of the many reasons why for 6 years and counting, people from all across the globe are playing and modding the games blessed with the power of Source.
I hope Valve never lets go of this one. Great graphics, sound, effects, and online support.