Thanks, P.P.A. and magnum12!
Magnum, I agree with you that SA2 is highly over-rated. The camera can be the most anoying in any 3D Sonic game, unless you just follow the path you are supposed to follow. The shooting stages are not so fun and I agree that Gama's stages where somewhat better, though not by much. The most anoying thing is the Chao-raising, which I can't describe with words how much I hate it! Design-wise, it's less horrible than in Sonic Adventure, but the fact that you have to spend much more time with the Chaos in SA2 than in SA1 in order to collect all embles, makes it even much worse! Biggest torture ever! However, although this is a matter of opinion, I think the hunting stages in SA2 are very good and creative. Much better than the ones from SA1. I wished there were Sonic-Style stages with the design of the hunting stages! I think the Kart Racing was also OK. The best part of SA2 is of course the Sonic-Style stages. I think most of them are the best in any 3D Sonic game. For this reason I still believe it deserves a high score, even though it is really a shame that only slightly more than 1/3 of the game consists of these stages. There are some really awesome soundtracks in the game as well. All in all, it is true that this game is way too over-worshiped and is very far from the best Sonic game ever created.
On the other hand, I think Sonic Adventure is also way too over-rated. The Sonic & Amy stages are fun, but, in my opinion, most of the time, by far not as exciting as most other stages found in other 3D Sonic games. The gameplay of the other characters is for the most part really not that interesting and especially Big's fishing stages are some of the very worst things ever happened to the Sonic universe. Furthermore, the game is way too easy and the Story Mode hardly provides any challange. It only gets challenging if you go for competition, but most players don't do that anyway. Also, the game is not much less glitchy than Sonic 06 is. The only reason that noone really cared back then, is because it was Sonic's first real 3D game and everybody was so excited and all. In my opinion, it has also the least interesting music between all 3D Sonic game. Overall, you can still get a lot of fun out of the game, if you at least try to do some SpeedRuns, but I think all 3D Sonic games afterwards have improved over Sonic Adventure in pretty much any way.
About Shadow the Hedgehog, I totally have to agree with you! I just wished all those people who hate this game just because Shadow uses guns in it and says "Damn" would open their eyes and realise how much effort was put into this game! Gunplay has already existed in Sonic games since Sonic Adventure. The difference here is that, in contrary to the Sonic Adventure games, the gunplay in Shadow the Hedgehog is really fun, and as you said, really adds a layer of strategy. The vehicles are also sometimes an interesting option, though not always; but if you don't like them, you usualy don't have to use them anyway. Collecting the keys and seeing what they unlock is also pretty interesting. I also think that this game has some of the most varied and best stages in any 3D Sonic game and the fact alone that there are 23 stages, all just for Shadow, and that there are no other useless playable characters, only makes this game even much better. No Big the F*cking Cat or any torturous Chao-raising. The music also kicks ass! If only the bosses weren't so crappy and were actually really fun, and if A-ranking had been more challenging, I had given this game a 10/10.