Coming from the Vibrant, I will say that I loved th escreen size on it, as well as the slimmer form factor. That being said, the lack of led notifications, a camera flash, non-functioning gps (even with "fixes", it was half-ass at best), no trackball (which made placing the cursor at specific points bewteen words very difficult), and Samsung's seeming unwillingness to commit to a hard deadline for a fix to any of the software issues described here and eslewhere, let alone a definite date for a 2.2 update, had made me nostalgic for an HTC device.
Unfortunately, when I got the Vibrant, my wife became the proud new owner of my carefully kept, rooted, booted, and scooted Nexus One, so I was stuck.
Personally, I really like it. It's like a Nexus one with a keyboard, without the colored trackball, with a faster processor, an edge-lit trackpad, slightly more girth, and a better gpu.