One big mess of irresponsibility and laziness.
The PS2 version of this game was obviously negleted to quality during the making. One of the first things I noticed was at the menu: you have to press O instead of X to make selections. It's known to almost all PS2 owners that the X button is the primary button for jumping and making menu selections. But instead of seeing the colorful menu, I was irritably thrown back to the title screen, where I had to wait another 10 seconds to find out which button to press to select.
The main mistake, however, is the lack of attention this version received. When I started playing, I realized immediatly that buying this game was a bad idea. There are many noticeable flaws that prevent me from enjoying the main aspect of the game, especially the horrible frame rate. I know the PS2 is slower than the Xbox and Gamecube, but this performance was rediculous. I've seen many games that have much smoother gameplay than this. To be honest, I don't see how hard it would be to match the game to the PS2's native framerate output!
Another thing I noticed was the bad sound quality and missing sound effects. The overall voiceover in the game wasn't half bad, but many sound effects lacked clarity and detail, making them sound like something from the Nintendo 64. Also, as I said, many sounds were missing, such as when you home in on an enemy, you don't here yourself jump or the enemy blowing up.
It's been over a year ago since I got this PS2 version, and now I have the Gamecube version, and enjoy the quality and fast frame rates of the GC version. When I first got the game, I had nothing to compare to, so I really didn't have an idea of how bad this version was. Now that I look back on it, it made me decide to write this review. Sonic Heroes isn't a bad game at all; in fact, I really enjoy playing it. But if bad quality and hardware limitations threaten to distract you from the focus of the adventure, then I say "Get the best version available, the Gamecube version."