While a good port for the most part, the Dreamcast version is still the best.
There are three big difference between this game and the 1999 original. First, the graphics have been noticeably been revamped. The game looks brighter and more colorful. The characters look glossier than usual and have a higher polygon count, making them look smoother. The environments got a few touch ups as well. Second, there are missions within the hub worlds. Basically, if you want pointless missions to keep you a little busier after completing the game, here you go. And finally, there are the Game Gear games. Some may not be that good, but others are actually pretty good and they add a nice nostalgic flare to them.
Unfortunately, problems from the first game remain intact. The camera can still be very bothersome and can lead to a few glitchy moments. Actually glitches are a little more apparent this time around. The collision detection feels a bit more inconsistent. This wasn't as prominent in the original, but here it can present as an issue. The voice acting is, of course, still crap and the lip sync still looks awkward.
PROS:
-It looks pretty good on the Dreamcast and it looks pretty good on here. The graphics have been bumped up a bit since '99.
-Same good Sonic action from the first
-Some of the bonus stuff is good
-Some of the music is still good
CONS:
-Camera is still a problem
-Big and Amy are still annoying
-Voice acting and lip sync still sucks
-Collision detection is a bit inconsistent
-A little glitchier
-Mission-based mini games in hub worlds are pointless
Bottom line: If you have never played the Dreamcast version of this game, this would at least be a good opportunity for people to see Sonic's first 3-D adventure in action. Even with some age it is still essentially a good game in the end. For those who have played the original and still have the Dreamcast, just stick with that.