Unreal3 is very similar, and all the differences between CryEngine 3 and Source Engine are about the same as the difference between Quake III and Unreal3. I love the fact that I can build shaders, scripts, etc with an in-editor visual system rather than outside text systems. And real time editing is awesome.
The fact that modern engines are no longer as heavily dependent on brushes really scared me at first, but now I actually only use brushes for floors, and maybe an occasional wall. I build 99% of the environments as a collection of static meshes built inside 3DS Max, ported into Unreal. The workflow took some getting used to, but the results are much better than using brushes.
Good luck with the learning curve! Took me a few months to get used to the differences but it was worth the transition!
And btw, if you ever need any help, reference materials, etc, let me know! I've studied the Desilu Stage 9 sets enough that I can lend a hand if needed!