After having completed Tony Hawk 3 and 4, I was looking forward to Tony Hawk Underground and can't stop playing since it came out. Underground is a lot like TH4, with free roaming levels and a lot of challenges, caps and secrets to find in each. There are a few changes though. The most notable is the ability to get off your board and walk/run around the levels, climb stuff and grab on to ledges. The extra feature is a nice addition when it comes to hidden item, such as some tapes are easier to climb to then skate and with this feature they can place anything anywhere, yet, the ability to do so, and leads to some unimpressive missions. There are some missions where you have to chase someone in a car (yes, you drive) and others where you just have to run around, which are pretty lame. They should leave the running and driving to GTA and focus on the skating. The graphics, although better are disappointing, once more an Xbox game which was not finely tuned for the system.
On the plus side, the new system for earning stats, in which goals are made (such as manual for 20 seconds, do 20 tricks in one combo, etc) is better than the old stat point system, this way, you have to prove that you are good and practice to get better at each aspect of skating (a la Aggressive Inline). The missions and levels are still very well made, with the ability to grind, skate, jump and interact with almost everything. In this version, the levels start out small and you unlock different parts as you complete missions. The loading is minimal and the few new moves, like wall push and wall plant are cool. Also the new signature tricks are as funny as ever and the ability to create your own moves is a great addition.
One disappointment is the create-a-character feature, which when compared to Tiger Woods 2004, does not have that many options. And the lack of Xbox live play, takes away some replay value and I'm not sure why this would be left out, but it was (and is why I rent, instead of buy).
Overall, if you like the series, grab it, if you hated 4, then pass as well. I highly recommend it (and suggest the hardest difficulty setting for veterans of the series).
Score: 9/10