I feel source is very much the same, but with some little and some big differneces.
One big difference is resources. you will never run out of resources in source, and if you do you bigger problems
One little difference is certain things like visgroups are improved, so much so they are kinda like a new tool, and drastically increases your workflow--especially quickhide and quickhide unselected--if you use them.
also it should be mentioned, the entity system is improved to an unbelievable level. It's a bit foreign at first compared to goldsource, but man, it possible to really do anything with source entities.