Final Cut Express vs. Final Cut Pro X vs. Final Cut Studio
FCPX, I've heard, is much easier but different. Its like a combination of FCPS and iMove: Simple, Elegant, Powerful, but overall different and in that sense incompatible with other FC project files. Its like OSX was at its time, or iMoive 8: "It breaks the line". If it's for good or not depends on you: how used you are to your workflow/plugins/etc.

Nevertheless, just like with iMovie or OSX, Apple wont go back and support whats old again, it will just keep improving, so I'd Final Cut X to be getting better with time whereas FCS is obsolete already. This plus the fact FCX is finally Cocoa 64bit and makes use of the latest Apple technologies might be enough for you or might not. It all depends on you.

Good luck!