Buy Android phone, install Android from source, have Nexus S -like experience?

I'm new to Android. I understand that although the Nexus S is built by Samsung that it has a stock standard Android image (whatever that means) and so it considered a "pure" Google phone. If I were to buy any Android phone and install a clean Android image from source (I assume this is possible... I heard it is fully open sourced) then do I effectively get a "pure" Google experience a la the Nexus S? Compared to the Nexus S, would I be lacking anything (software-wise)?