Upgrade of Pokemon Gold/Silver
All Pokemon Crystal basically is its just an improvement of Pokemon Gold/Silver. Pokemon will be at different locations with different occurence rates. Game features from Pokemon Gold/Silver such as Pokegear. clock, eggs, etc; will be intact in Pokemon Crystal. Pokemon Crystal will also have 251 Pokemon with basically the same storyline as Pokemon Gold/Silver.

Male or Female Trainer
During the beginning of the game, you will be able to choose either a male or female trainer.

Find Suicune Easier
Once you wake up the Legendary Dogs at Ecruteak City, Suicune can be seen physically, but not in Pokedex until you battle it.

Ho-oh and Lugia
Ho-oh and Lugia will be available in the game.

Unown Puzzles Changed
It wouldn't be smart to put back the same puzzles that many people have already solve already, so the puzzles are replaced with new ones.

Location Notification
When you enter a new place such as a city or route, the bottom of your screen will pop up a message box telling you where you are currently. When you enter a different place, this process will happen again.

Pokemon Animations
When in battle, the opposing Pokemon will animate; meaning it will actually move when not attacking. Nothing comparable to Pokemon Stadium, but its better than the Pokemon staying still sitting there.

Other Information
Pokemon Crystal will only run on Gameboy Color. The game will look very nice since it is designed only for Gameboy Color. You can send Pokemon from Crystal to your Pokemon Stadium 2.