The review praises the keypad which I'm sure everyone at this point knows had manufacturing issues when it was released. The keypad is very flat - most of my friends describe it as too flat. My girlfriends can't use it effectively because of their nails; the guys don't complain about that issue as much.
If you have the S500i I would highly recommend using the W580i firmware on your phone. The hardware is virtually identical with a small difference in features. Using the firmware gives the S500i the superior Walkman media player instead of the clumsy one that is built in.
Mysterious Green is the nicest version imo. It would be cool if the phone looked up your weather information online and adjusted the flash themes to match it (e.g. raining outside and the flash theme shows rain). The way it is now is random.