It's basically the poor man's Sonic Generations. Only for fans and those who can't get enough of the console version.
Aside from being impressed with the 3DS' capabilities, the first thought that came to my mind upon seeing the first static cut scene was "poor man's edition", and that's exactly what this game is. Poor presentation, which makes the dialogue seem like it harkens back to the archaic text-based PC RPGs, forces you to imagine what exactly is going on. And not in the comic book fashion, I mean the character models just stand there with random voice clips spouted out that most of the time do not match with the dialogue and cause confusion.
The levels in the game, aside from the first, may not be featured in any other version, but that doesn't necessarily mean they're good or as good as the console version. Classic and Modern Sonic's level differences are barely noticeable here. The main difference is Classic is more platform-based while Modern is faster, in a sense, with much more chaos in the screen going on. And keep in mind that Modern has no 3D levels aside from the bonus chaos emerald one. I expected more from this game in terms of content, atleast having proper cut-scenes through compressed scenes from the console version. I can't shake the feeling that this version is a victim of development time constraints.
DO NOT under any circumstances play this version before you play the console version first. You're missing out on a great package. Even if the 3DS version is your only means of playing this game. As a fan, you owe it to yourself to give the console version a go. This version is the pre-telecast event, the main gala is the console version. Happy Birthday Sonic!