"bad" is a bit of an overstatement, but it's not as fun as the console versions since classic & modern feel a bit too similar at times (really, it's just that modern can boost, classic can't) & doing those missions is tedious because for the most part, they can only be unlocked by play coins.
....it also only has Sonic Rush representing handhelds & is the only exclusive "game" in the 3DS version. But for $12, it's an alright game worth checking out if you want to see how they did certain stages like Casino Night Zone, Mushroom Hill, Radical Highway, etc. since it has stages not in the console versions.