Even if you don't care about Rollerblading, give this game a try.
THPS4 has alot going for it and its a pretty widely liked game and franchise, no doubt about it. But for me, I prefer the gameplay of Aggressive Inline over THPS4 anyday.
The only real flaw on Aggressive Inline compared to THPS4 is that lack of a customer skater creation tool. I really enjoyed creating my skater and picking my board etc. However, in AI, you only get to choose from a list of professional bladers and a few generic characters, each with their own strengths and weaknesses that you can steadily improve over time.
As for the gameplay, I really didn't like THPS4 that much. It just seemed like the controls were vague and the engine didn't handle collisions very well with dramatic bouncing sometimes and faceplants other times whereas AI you really know when and why you wipe out. The controls are smoother and you really get a feel for the speed of your character. The levels offer a variety of challenges from the basic "Grind that lamppost" to photographers asking to take your picture while you do a certain grab or flip in front of them.
The music was good but if you spend alot of time playing, it will get old, no doubt about it. They could have had about 4 more tracks in my opinion to keep it varied.
The graphics are very good with skater movements looking real, jumps, flips, and grinds look nice although wipeouts offer a stupid large amount of blood that I found unnessecary. There is no option to turn off the blood. If there were, this could easily be a game for most anyone. Replay value is pretty good because there are alot of secrets to unlock that open things in later levels. Many of these will be skipped in the early stages of a game and you'll want to go back to certain levels much later in the game and its fun to see older levels after your skills have increased.
The skill system is such that the more you do certain moves, the better you skater gets at them. This allows you to pull of the move easier and that allows you to chain more moves together into large point combinations.
Its strange that I liked this game much more than THPS4 simply because I have never really enjoyed rollerblading, yet growing up, I used to skate board all the time. I really thought the Tony Hawk games would give me some of that old skating nostalgia but they didn't. I just got frustrated with the controls and collisions and never really felt like I was skating. Whereas with AI, I really feel like I'm rollerblading around and pulling some sweet air.
So, check you local barbain bin for this game. You can pick it up for $10 or less most likely. Its a fun game.