Personally I'm happy with my Evo. While there are improvements to be made, I don't expect to see enough of them in the next installment to make me want one. Actually I hope the next installment is later, a) so we get more android updates(since the evo will be HTC big sprint phone). b) so the Evo 2 is a serious upgrade an not minor changes.
My list of changes would be
a) Better battery life. The battery life is ok, but it could be better especially with 4g. However just a small increase in battery won't make me buy a new one.
b)More physical memory. Yes we can install apps to SD, but there should be more room. Again, not buying just for this.
c)Dedicate GPU/better gaming performance. While the Evo is fast for processing data, its not the greatest for gaming.
d)A screen that is better in the daylight. Maybe amoled, or whatever they can do to make it better.
e)higher resolution screen. I mean, who doesn't want this.
f) Faster camera. The quality is decent enough for a phone, but I'd like it to be faster.
Things I do not want.
a)Physical keyboard. Phone is huge as it is.
b)Bigger screen. Again, the phone is huge as it is.