Well, It was fun for me when it came out. I got my copy of the game and would play it for hours and hours just creating different beats. Back then, my PSOne was still alive. (it's dead now RIP PSOne :y )
What I like about this game is that it is very easy to mix different types of tune loops. You do not have to be a music genius to match good tune loops. You just gotta have a good ear, because not all loops combined together will make a good sound.
On the video below I show my tune which I just had to download it. I created this tune in approximately 5 minutes or maybe less. One advantage point this game is better on the PSP than on the PSOne is the ability to store much more data with large PSP memory sticks (mine is 4 Gigabyte), than PSOne memory cards. Plus you do not have to worry about disc scratching (damaging the game). All games residing in the PSP memory stick won't go to waste unless your memory stick breaks. But on the opposite side, on the PSOne, you could get short samples of audio from any music CDs, which for the PSP, you cannot. Bummer!!!
Overall MTV Music Generator On the PSP Rocks, and for all who have CFW on their PSP this is available to download using your PSOne emulator(Popsloader)