This is a good game that has tons of challenges and fun levels. It gives you a sense of speed while giving you a good challenge at the same time. With 5 usuable characters (4 in story mode) you can always do something different for anything you're doing.
These are some of the best graphics I've seen on the PSP so far. You have good backrounds, you can give all 5 characters lots of different outfits, and even while you're going fast it's easy to see great detail in objects all around you. And the special effects of the attacks you use are great.
The sound is pretty good, but there are times when you can tell they were added at a time just slightly off of when they should've been. The voices aren't overly well done, but they're there anyway and we've gotta give sega credit for that. The music in the boss battles are great too, and the victory tune is pretty good despite it being a remix of the one in Sonic Heroes(PS2, Gamecube, XBox)
There are tons of challenges to be completed, plus 4 story modes that you can have fun with. Also there's a card collection to keep you busy trying to get just one card for a LONG time. So you know you'll be playing for a long time. And the best part is you enjoy doing those challenges trying to get the one card you're looking for because you have a great time trying to win the level.
This game lasts a long time with so many challenges and story modes that give you 3 stages of a level for every level you do. So you know you'll be playing for a long time just constantly going after a challenge one at a time. But the challenges are... Well challenging so you won't get bored.
Overall this a great game for the PSP that definately makes my good books. But of course it's a good idea to rent it before you buy it just to test it out. If you're not a fan of Sonic games then I don't recommend this game but if you've been playing Sonic for a long time like me, then I know you'll love it.