The battery on this phone is good enough that you don't have to think about it. That's the definition of success in my book. Some things obviously will kill it, like Navigation, but on an average-use day I never think about my battery at all and just plug it in at night. I had a Thunderbolt briefly and it sucked having to cripple the thing and do tricks and still be worried all day that I was going to get caught with a dead battery, which did happen. I don't know how the X is batterywise but I know this one shouldn't be a problem for the average user.
Again, not having had an X, I can't compare the browsers, but the browser is another thing I don't think about. I just works and there you go. If you don't like it or need more bells and whistles, you've got Firefox, Opera, Dolphin, etc.
I have found the dev support for this phone to be less than I was thinking there would be. I guess it's not as exciting as the flagship phones. But with that said there are still a number of good ROMs out there, such as Cyanogen, Virtuous Unity, and others. Check the Dinc2 development thread over at xda to see the most popular ones.
There was root for 2.3.3, but I think as of the writing of this, there is still no root for 2.3.4, which is what yours will come with if you get one at this point. However there are instructions at xda (and maybe also reflected here in our Dinc2 root/ROM subforum) on how to downgrade your hboot, which apparently makes it once again rootable.
One drawback of this phone is a fairly quiet and tinny speaker. And I also feel like the earpiece is a bit quiet. Some have complained of reception issues, but you know how that is - very subjective. Some have complained of the default keyboard but again you've got plenty of free or cheap options there.
Otherwise it's a solid winner. Feels perfect in the hand. Perfect.