I got the D4 coming from a D Inc 2, and before that, an OG Droid. I love the QWERTY, screen size is perfect for me and the battery life is great when you combine it with Juice Defender or Smart Actions. Even without them, you would probably get a full day out of it if you don't use LTE too much.
Comparing to the Droid 2, the screen is a bit bigger obviously, and the blur is different. I have a friend that came from a D2 and he loves the D4. The build quality is much more thought out on this one compared to the D2.
Any other questions? Hope this helps.