For example, in one of Sonic's missions, all you have to do is find a particular man standing in front of a hamburger shop in one part of the city and then bring him over to the train station.
In addition to the main game and the Game Gear unlockables, Sonic Adventure DX offers a mission mode where you can venture around the city and temple areas in an attempt to complete a series of relatively minor missions. It's a nice extra to have initially, but once you realize that most of the Sonic Game Gear games weren't all that great to begin with-and that some of them actually have some slowdown issues-your interest in collecting enough emblems to unlock all of them will diminish. You can get these emblems by performing well in individual levels, or by simply searching for them in various parts of the game.
While that was pretty much the only incentive for playing through all the levels in the Dreamcast version, Sonic Adventure DX attempts to add more motivation by throwing in some Game Gear Sonic games that can be unlocked by acquiring Sonic emblems. In any case, the missions featuring the secondary characters aren't as entertaining as the ones that feature Sonic, but you'll have to play through them if you want to unlock the last level and the game's real ending. Tails' missions will have him racing against Sonic, while Knuckles will have to retrieve pieces of the chaos emeralds. E-102 offers a slightly different pace as well, since he's a relatively slow-moving robot equipped with a cannon for destroying various types of targets. However, some of them are vastly different, such as Big's missions, which have the enormous purple-and-blue-striped cat attempting to capture his pet frog.
It's worth pointing out that some of these missions overlap, and some are nearly identical to the ones found in Sonic's portion of the game. In the beginning of the game, you can play only as Sonic, but whenever you meet a new character-such as Tails, Knuckles, Amy, E-102, or Big-you can start playing as that character in a series of separate missions. The portions of the game that focus on this hub area seem a little pointless at times, particularly when all you have to do is take a key from one location to another, but most of the time it simply functions as a tool for advancing the plot. Sonic Adventure DX is structured a little differently than its sequel, Sonic Adventure 2 Battle, in that there's a hub area that Sonic and the other characters in the game have to find their way through to access the actual levels. Sonic Adventure was originally released on the Dreamcast in 1999. For everyone else, Sonic Adventure definitely has its moments, and some aspects of the game have held up reasonably well over the years, but it still has its fair share of problems, ranging from an unstable frame rate to some inconsistent collision detection. Unfortunately, if you've already played the Dreamcast version, these extras definitely aren't worth your money. Sonic Adventure DX is essentially a port of the original Sonic Adventure, which launched alongside the Dreamcast in September 1999, but Sonic Team has thrown in a few extras to entice those who played the Dreamcast version and to extend the replay value of the game as a whole.