I came from the Epic Touch. Not worth $550 for better connectivity IMO. However, better connectivity is pretty much the sole reason for me to upgrade (also to not get the Galaxy S3 instead). GPS is significantly better. Using apps like GPS Status I can say that the signal locks quicker, more satellites are in view, more satellites are in use, SNR is much higher for the same satellites, location is more accurate and it has never failed to get a lock in any situation. My Epic Touch frequently would not get a lock until I restarted the phone. All other radios also seem a better overall.
Is the handset that much better? Yes but not $550 better. What is better is the hardware and not the software. Overall UI is not as smooth as TouchWiz and Sense 4.0 has its issues. You will notice the difference in everyday use (UI stutters, web browser laggy, etc...). All software issues. I love the feel of the phone. Very solid. Samsung plastic never bothered me until i got use to the solid feel of the new EVO. Same goes with 720p resolution. I didn't care for it till I got use to it not everything less looks blurry. I also miss the kickstand.