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.
It's my favourite engine, so why do I give it only 8 points? Not because it does not have the best graphics or something like that. Content-quality is something that you should find in game-reviews, not the ones for the engine.
I give it only 8 points because it is a pain in the a** to use. Why do I have to sit through a long (map)compile before I can see if I changed the brightness-value of one single lighting-enity correctly? Why can't I add materials via drag and drop and edit its properties in realtime? Besides that it's really getting old. I don't need graphics and such big maps like Dunia has, but with Source I have to cut big maps into small ones or I run into its limits if I make it detailled. Look at Cinematic Mod. It pushes Source beyond its limits and still looks crappy against Crysis, while having much higher system-requirements. That's one of the cases where you see how old Source is and that it wasn't made for the quality-standards of 2011. The standards raise faster than Source. Back then, when Source got relased, it was unbelivable that it has Radiosity, now games do that in realtime. Just as lighting. "But Portal 2...", you might say. Portal 2 still has not "real" realtime lighting, because props still arent lit properly and you still have to compile.
This review is not to bash VALVe or Source, I am trying to be objective here, because I hate people that defend Source in points where it is just stupid to do so. It's time to stop being a fanboy, stop being biased and just go on.
Source is an extremely versatile and powerful engine, and Valve have done some very impressive things with it. However, the tools for it, especially Hammer, are very outdated and not user-friendly. On the upside, you are given the source for HL2 with no sandboxing, which is certainly an advantage over Unity, where you are forced to use sandboxed scripts. However, the user-unfriendly tools make it difficult to quickly prototype or start a game in the Source Engine.