My wife has one, so I use/support it a lot, but it's not my main phone.

Form Factor: Perfect. This is huge. I love the small, compact size, and the physical keyboard.
Overall UI: Awesome
Web: Perfect
Videos, camera, contacts: Great
GMail/Calendar Integration: Perfect
IM/SMS: Perfect
Games: Minimal selection. This could change of course.

GPS: Good enough to replace my TomTom, but the Android 2.0+ stuff I've seen is definitely better. I hate that Sprint Navigation and Google Maps are separate applications that don't integrate. The Google Maps app is way better at finding what I'm looking for, but I can only get the guided directions in the Sprint Navigation app, and I have to manually write down the address and re-enter in Sprint Nav.

Battery Life: Terrible. Biggest problem. I don't have solid numbers, but my wife has to charge every single day and often multiple times per day.

Glitches: Terrible. We've had two hardware problems that required us to exchange the whole handset and we have recurring software glitches that require us to restart the device. Honestly, though, after heavy use, most phones I've owned have had some glitches (my dumb phone is definitely worse: it will sporadically just shut off every few days for no reason even with a full battery).