Sonic Heroes is a great game that is often underrated. It is probably the closest thing to the original game (so far).
There are a couple of flaws that, once you get used to them, won't detract a lot. With the game I have, sometimes it acts as if I've pressed a button twice when I only pressed it once. This is probably to due the copy I have or my controller. The camera takes a while getting used to, but once you get it, you'll use it seamlessly.
Another flaw is that when some of the ‘power’ characters attack, they move around a lot and often you might fall off a platform and die. However once you get used to all the level-ups and their effects, then it is not much of a problem.
The game is relatively short compared to other games nowadays but you can choose from 1 of 4 teams. All the teams go through the same levels but there are different paths and obstacles each team takes. Every level has a mission that the team must complete, it is often just getting to the end of the level but Team Chaotix has a different mission each level (eg. Destroying 100 robots).
The biggest disappointment for me was the 2 player mode, if you have the time to unlock all the different mini-games then it isn't that bad. It would have been nice having a couple more levels to choose from.
The music is excellent, like in the classic Sonic games. Some levels are also inspired by levels in the classic games and there are a lot of vibrant colors.
If you like Sonic or if you don't mind a couple of little flaws then you should get it. Trying to get 100% is quite a big task, but is possible if you play it long enough.