Do you remember Sonic The Hedgehog and Sonic The Hedgehog 2? Someone at Sega probably hopes you don't, because the environmental designs Sonic 4: Ep. I are lifted straight from those games. Splash Hill = Green Hill. Casino Street = Casino Night. Lost Labyrinth = Labyrinth. Mad Gear = Metropolis. There are some mechanical variances in the levels, but by and large, the world has been almost completely ripped off. Even the boss fights have been recycled; save for a few new moves, they're identical to their 16-bit counterparts. At least the game as a whole looks decent. Recycled environments aside, the game occasionally goes out of its way to remind you that we're no longer living in the 16-bit days. Little effects have Sonic running towards and away from the screen; it's nice, but I think the game would have been better served by the original engine. Oddly enough, the weakest link in the visuals has to do with Sonic himself. His footfalls rarely correlate to his actual speed.
Old-school Sonic games are known for catchy, irresistable soundtracks. Sonic 4: Ep. I fails in that regard, but the music is by no means bad. It sounds like something you'd hear from a Genesis game, but without the audio-related weaknesses of that platform. This music certainly belongs in a Sonic game, but it compares poorly to the original stuff. The sound effects have been faithfully preserved; fans wouldn't have it any other way. If they replaced the classic ring sound (or even the bizarre bass-heavy death sound), it just wouldn't feel like a Sonic game. The audio's biggest achievement is the voice acting, or rather, the complete lack thereof. Sega has wisely opted to shut Sonic's trap, but so much damage has been done in this department that I'm still slow to forgive them.