I'll give you a couple basic examples.
Functionality----
Mail: Not true IMAP when IMAP is selected. Can't chose mail path prefix. Can't chose folders
Design----
Text Messages: Buttons on the right side(EVO) are easily pressed accidentally, interfering with text messages. No send button in landscape mode
All in all----
Basic, core OS fixes are not addressed, but pay apps are made instead
This is without getting too deep. I really can go on
Well, your second issue (the buttons) has nothing to do with the OS and everything to do with the phone you chose to buy. Maybe you'd rather have true buttons similar to what the Droids have (which I think are actual buttons you have to press vs. touch ones). Not sure how long you've had your phone, but it took me all of about a day to get used to them and rarely press them accidentally now. Anyways, it's a hardware (or arguably a user) issue as opposed to an Android OS problem.
I don't use IMAP, but use Exchange and Gmail and have options for folders. Not sure what the issue is with IMAP since I've never used it. I'm not sure, but perhaps another email app would address your issue (like K9 mail, for example)
To be honest, I've never had an iPhone, but have an iPad 2, which I assume is a similar experience to the iPhone. I personally pretty much despise iOS. No Flash, no options for alternative keyboards, only one email signature that gets used on all of your email accounts (although there may be an app to correct this), no widgets (just screen after screen of icons), pretty much everything about the app store blows chunks, other than the apps themselves (navigation, searching, filtering, etc are all just a horrible horrible experience), etc. About the only thing I like about it over my EVO is the bigger screen. I really only have it because the company bought one for me.
Regardless, you should be using the OS that suits you. If Android doesn't meet your needs, use iOS.