Basically in v1 all ram initialization code was written in assembly, while in v2 it is written in C. There's also only one device tree instead of a static and a dynamic device tree. Plus, there's ACPI support (because there are machines out there that can't be booted without ACPI anymore)
Video is in there as well. Getting video to work in V1 is quite a bit tricker than in V2. If you are wanting video then porting to V2 is probally a good idea.
-- Richard A. Smith