I am very pleased with the myTouch! I would describe it as a mix of the G1 with the Samsung Behold.
It is fully touch screen, with a track ball and easy access buttons for the menu and home screen(s).
It's as lightweight as the behold (thinner and lighter than the G1) with the same exact screen size.
The internet is fast, and what I am most impressed by is the quality of the youtube app, which comes built in already - usually youtube videos on phones are slow or buffer constantly. The video quality is still fuzzy as any phone, but it didn't skip or buffer ONCE, its GREAT.
I like that it has the "work email" app built in, so you can sync with Microsoft Exchange/outlook.
I wouldn't go as far as saying the phone is worth the $500, thankfully I was due for an upgrade and got it for $200.