Much quicker. It can handle a lot more before getting sluggish (with twice as much RAM). It is a prettier phone with softer edges and the metallic blue and blue parts of the keyboard make it more appealing. It is as heavy as the original, and it feels very solid.
The keyboard no longer has a shift or alt on the right side. I miss that since I am someone who is more used to a typical keyboard. I like the arrows better than the directional pad. I make less errors with typing on this phone, so that is a big improvement.
Supposedly the wireless is better than the original. It seems to be much snappier with web pages, but that is probably more due to Froyo and the better processor.
Having 256mB was one of the greatest limitations of the original Droid.
I will have to decide whether I will want to root this thing. I'm pretty happy with it right now, except I would like to be able to better utilize the 8GB of phone (non-SD) storage. 7GB is sitting there unused, and I would like to put some videos on it. I have yet to find any app that allows you to create a folder or put a file onto the phone (non SD).