Sonic Gems Collection is a good compilation of your favorite old Sonic games.
Sonic Gems Collection is definitely one of those "odder" games you'll play, but nevertheless, it's a good run. The graphics and sound from the game are great. They are close, if not, the same as the original games, bringing back good memories from the good days. An addition to this game from other games is the "Museum." The Museum is collection of art and screenshots from past Sonic games and also has some remixes and tunes from older Sonic games. This is probably the main attraction to the game, as it requires GREAT work and has a large difficulty to earn everything in it. I completed everything needed to complete the museum, but many will be disappointed, as the only real reward you get for completing it is a picture of Sonic and Metal Sonic. There are many hidden secrets in this game, and it will keep you playing it for a while. This game has a fair amount of games in it, the three most noticeably great ones being Sonic CD, Sonic R, and the rare and arcade-exclusive Sonic The Fighters (in North America, also known as Sonic Championship). If you plan on buying this game, the only replay value you'll receive out of it would have to be the three games recently mentioned.
Overall, Sonic Gems Collection is a great collection of classics for anyone who hasn't played a lot of Sonic's titles yet, and for those who have, it is worth renting or playing at a friend's place.