I'm inclined to think you are right. Sonic Adventure 2 is great nostalgia, and Sega did a good job of cramming in a ton of different ways to play the game without it being too much annoyance. Plus the Chao are a good time waster too.
So many other Sonic games are just tedious and slow. Even on the Eggman/Tails stages you can feel like you are rampaging through a level quickly in SA2 (though the Knuckles/Rouge stages ARE tedious). There's a lot you can find to like in SA2, they never really made another game like it.
The day levels of Sonic Unleashed feel fast and good but they are too short. I also grew up a Mario boy so playing classic Sonic is frustrating lol every time you try to go fast on classic Sonic they put spikes and enemies in the way to punish you.
If nothing else the SA2 soundtrack is 10/10, there's something for everyone.