Surprisingly competent throughout, daytime levels are a masterclass of 3d sonic. The werehog levels, while a bit half baked were still surprisingly fun. I did not care for the seemingly endless waves of enemies disguised as level design though. The concept of combining night and day mechanics into one level is super interesting in concept, however, eggmanland ends up a bloated trudge through the worst mechanics from each gameplay type. The boring 2d sections and quick time events for the daytime segments, and the onslaught of enemies and janky camera of the werehog segment. The medallion system is such a cheap gimmick for forced replayability. There is no reason I should have to walk slowly through a daytime stage just to look for medallions. Also good lord this game needs a remaster, the daytime levels can be borderline unplayable when the frames drop.
All in all a fun game and perhaps spoken of too harshly, having said that I cannot imagine myself replaying the werehog levels any time soon.

Sonic Heroes is in contention for one of the worst games I have ever played. This game is not even necessarily broken or unplayable. Obviously, games like Sonic and the Black Knight, Secret Rings, and Boom are much worse.
My problem with Sonic Heroes is that it has so much potential that is not seen through in any aspect, the movement being the worst offender. It is so slippery to the point where you have to be on edge the entire time you're playing. This also becomes incredibly frustrating because of the lack of invincibility frames. Consistently during my playthrough I ran into an enemy then continuously took damage since I did not have enough I-frames to get out of the way. I died several times to this either during boss fights or when I was far away from a checkpoint.
The special stages might be the worst part of the game. Bringing the key all the way to the end of the stage becomes extremely difficult after the first couple zones. The mechanic might have been fine if the key dropped like rings and could be picked up after taking damage. The only way I could get the key to the end of the stage was through the heavy use of save states. The special stages themselves are borderline unplayable, making turns is impossible and grinds your speed to a halt. Making any sort of mistake in a special stage means you have to try again in the next stage. This makes an endless loop of failing a special stage and then having to play through a harder stage and risk losing the key for another try at the chaos emerald.
The part of the game that might be the biggest disappointment is its use of previously established mechanics. The momentum in the Sonic Adventure games were the best 3D Sonic has played in the series. Heroes' momentum is a strange, slippery amalgamation of previous games. The grinding mechanic was essentially ruined in this game as well. The leaning and crouching from SA2 made rail grinding fun and satisfying. In Heroes, the only way to build speed is to spam a button, leaning in this game hardly does anything.
A concept I do think is well performed in this game is the level up system. Fully leveling up each character and blasting through enemies does truly feel satisfying and almost feels like a reward for putting up with every other aspect of the game. Seaside Hill through Power Plant are honestly well made and fun stages that work well enough with the game's mechanics.
While Sonic Heroes is not the worst game I've ever played on a technical level, it has made me feel disappointment, sadness, and frustration like no other game ever has.