I do not believe that it was the downfall. It was a test into the 3d sonic world. I loved the multitude of characters you could be and the difficulties and story line that changed with it. As for the swordplay game( I cant remember the name- that's how much I didn't like it), I believe it was the downfall of sonic. Unleashed wasn't bad, but it did not give sonic the extra push to keep it alive. If Sega can use their brilliant minds to think of another amazing sonic game, It might just be the AED to revive sonic, because he is not completely dead, partially because of this amazing website.

I think it was decent, but Shadow the Hedgehog was atrocious. We get it man, you're edgy. Swearing doesn't make you look cool.

That's what I thought but I'm not sure if that was the start of Sonic's downfall .
I need to research this . The thing that I didn't like about Sonic Hero's is that
for every story there are recycled cut scenes . It was annoying to watch the
same cut scene over and over again.Team Chaotic was a waste of time.
You had to look for hidden items throughout every stage. Some of the stages
were too long or annoying to search. The specials for every team were blah to me .
I loved the special stages . The music always got me hyped to do the stages . You had
to chase the chaos emerald and the emeralds got faster and harder to catch which was
awesome to me .Team Amy had no other objective than to find sonic so I found it boring to
do their stages especially since the difficulty is easy. I found Sonic's team the best team to
play in the game than comes Team Dark . The difficulty for Team Dark is hard and it became
challenging at times. The last boss .. I expected more but it was alright I guess . It was
some giant metal sonic ... " thing " . * sign * Its an alright game in my opinion but the
replay value is low . I didn't play the game again until the beginning of last year .

NOPE. Sonic Adventure was. Maybe 3D Blast. Adventure series is fun to play, in a sort of nostalgic-laughably terrible way. I like heroes (nostalgia), but it is pretty terrible critically.

The worst Sonic Game was Sonic R. I don't care how young you were when you played it. It's horrible, buggy, has a slew of problems, balance issues. The only thing good about it is the Music and only because it's campy and upbeat, even though the music is terrible too. Sonic R was the first TRULY 3D Sonic Game and it set the tone for the whole series of broken Sonic problems.

Thankfully, Sonic is awesome again. Sonic Colors and Sonic Generations are two of the best games I've ever played, let alone the best Sonic games I've ever played. I'm glad Ubisoft took the Sonic Curse and has started making terrible games after they made Sonic Chronicles.

No really, every Ubisoft Game before Sonic Chronicles was awesome and every Ubisoft Game after Sonic Chronicles is terrible.   

I don't think it's the downfall of the series but that was the last good Sonic title before things went upside down for the Sonic series.

In my opinion, Sonic Heroes wasn't really a sonic game.

It played like a beat'em up, and was long and gimmicky. Playing through an area the first time with say, team shadow would be really fun, but by the time you reach the fourth team, it become tiring.

Still, It was a continuation of a long slope, that wasn't very steep. Sonic Adventure was a great game, but had problems, Sonic Adventure 2 was pretty good, but had problems as well. The cycle continued until the series hit rock bottom at Sonic 2006, and started climbing back up with Sonic and the secret rings. That game wasn't great, but was better than '06. Sonic Unleashed was alright, but had some problems. Then Sonic Colors came out, bringing the series to being better than the adventure games ever were. Then Sonic Generations cemented the series finally not breaking the polygon ceiling, but destroying it.

no it fell as soon as shadow the hedgehog came out sonic heroes was a great game with loads of characters and fun levels and awesome soundtrack

I don't think that Sonic Heroes was the downfall of Sonic, I had a LOT of fun playing it.

Personally, I think the downfall of Sonic was "Shadow the Hedgehog" 

Yes and no. Yes because many people treated it as a unworthy successor of the adventure series and began disliking the Sonic games because they did not live up to them. Personally, I would have to disagree as while it is not as good as the previous installments, it is as good as they could have done with it minus the glitches. Why I say no is because if we are counting main canon games only, I might have to say Shadow the Hedgehog was the start of the downfall. Granted the idea of making Shadow more impressive than he was does seem like a good concept, but the execution is so pitiful. The thought of a branching story-line and multiple endings really sound good, choosing if you wanted to be good or bad, however this is ruined by the fact that the canon ending forces you on one alignment. While the series has gotten in a downfall, I think it really improved with Colors and Generations and the series is looking very strong again for the future.

I'd have to say no. I kind of have a hard time caring about Sonic nowadays (the first time I really started to get into Sonic's 2D games was the iOS port of Sonic CD, and I've never really played any of the 3D ones except Colors, Generations, and a very tiny bit of Unleashed and Adventure 1 DX. Sonic Heroes looks like a pretty slippery game, but I wouldn't say it was a downfall. I think Sega is actually starting to make a comeback with Sonic, especially now that they are teaming up with Nintendo for a new Sonic game on the 3DS. Sonic never really had a complete downfall (even though I really cannot believe how much 06, Chronicles, and Secret Rings sucked).

I thought Sonic Heroes was a pretty good game if you tell me, but the game that really caused Sonic’s downfall is Shadow the Hedgehog and Sonic 06, those are the game that caused it.

No, I think that it was a fun game to play and I certainly don't think it is the downfall of sonic or sonic games. It was fun to play and I liked it, the game itself was pretty good. I think that everyone can agree that sonic 06 was the downfall of sonic games, it wasn't that good. So overall, I think sonic heroes was a good game and it was not the downfall of sonic games.