It's basically the same as my Droid Eris. I mean, not really because in terms of hardware specs they aren't close at all. The EVO is far superior which means it can do some much cooler things now, and will be able to do many more cooler things in the future.
But they are both HTC's, and both run Android via Sense UI. The build quality on my Droid Eris is fine; I haven't had any problems with it. I don't really use the track ball much, but that's hardly a negative. I liked Sense UI more than stock Android, but I ditched it anyway because I like Launcher Pro even better. But you can do the same thing with the EVO if you desire.
The battery life on all Android devices leaves a bit to be desired, and it is exacerbated by my one HUGE pet peeve with the device which is that 1) many applications never actually close and 2) they all want to run in the background when often they don't need to and you can't tell them to stop, and 3) they all want to use your GPS and constantly send or receive information for really no good reason at all.
Which means that you may not even get 6-8 hours on a charge without some active management. It's not like you need to run it in airplane mode all the time, but you will want to get some kind of task manager/app killer (there are several free ones) and use them to manually turn off a bunch of silly services and apps you don't really need.
Not a deal breaker to me by any stretch, but it IS annoying. For me, I like to stream at work so the lack of battery life compared to other devices is not a big issue. I don't think there's any phone right now that could last all day if you stream audio on it for 3-4 hours straight. So I have one charger at home and one for work. That solves the problem for me, but if you are the kind of person who mostly wants a cell phone for calling people and you'd rather have the convenience of just putting it in your pocket and carrying it around all day and only charging it at night, it's something to consider.