Well, it's well designed and works as a great entertainment device for music, games, and it works well for surfing the web with wifi... and I think it's argueably the best value in terms of what you get vs. what it costs. Movies, games, applications, email, internet and music... it's like a portable touchscreen laptop when there's a WiFi connection nearby...
...but if you are looking for the cons:
1. it's big for an MP3 player
2. it's expensive for an MP3 player
3. the battery is non-removeable - which means some day it will have to go back to Apple for replacement
4. it's capacity is small for an MP3 player - especially compared to HD-based players
5. it doesn't take removeable SD/CF memory cards
6. it will only sync movies and music to one computer
7. it sync best with iTunes - which is not very nice if you are on Linux.
8. in the past, major firmware upgrades have not been free.
Still, if you want a portable entertainment device and internet device that happens to play music, I think a Touch is hard to beat.