here's what I recall liking about the Evo during the few days I had it:
1. haptic feedback
2. widgets
3. faster 3G
4. nice, big screen; more on-screen territory
5. customizations
6. actually liked the physical size
Here's where I found it lacking in comparison with the iPhone 3GS (at the time) and certainly now, with the 4:
1. iOS UI is more elegant: smoother, faster, more accurate scrolling and pinching (although HTC Sense wasn't too shabby).
2. The Display (but again...the Evo's screen looks good, too).
3. Customization has its price...Android menu system isn't as intuitive (not a huge minus, I must admit).
4. Maneuvering around the address book/contacts list was murder. I recall especially missing the ability to go from the A's to the Z's with the touch of a finger.
5. iPhone 4's unified email inbox wins....no contest. Android doesn't have one, and the best 3rd party app I found was second rate at best.
6. Evo battery life SUCKED.
7. Constantly killing apps to try and improve #6.
8. Did I mention that battery life thing?
9. I missed the integration with iTunes.
10. Wasn't crazy about 4G. Takes much too long to find a signal, then when it finds one, it is to the battery as a 70's muscle car to a gallon of gas. I just kept it turned OFF. Didn't need it anyway. Sprint's 3G, where I live, is considerably faster than AT&T's.
I found the apps stores to be a wash. Unlike many, many iPhone fans, I'm not starry-eyed over the App Store. I think that 250,000 apps, or half a million, or whatever the count is today, is a few hundred thousand too many. I found an equivalent on the Android Marketplace (Market? I forgot already) for everything I actually used on the iPhone. YMMV.
I liked the Evo. I think Sprint's combo plan for it is truly remarkable, and no one has it beat, certainly not AT& (cough) T. It's a good enough phone that I might've kept it, despite the fact that the iPhone 4 beats it on my own list, if I could have broken the AT&T umbilical chord. For reasons of my wife's, though, that turned out not to be possible.
Hope this helps.