Atari - 1983
Machine: Arcade, and many others
Some say this is just PacMan in 3D, but that is to do it a huge injustice. Then again, it basically is. What you have to remember is that back in the early days PacMan wasn't a game it was a whole genre and Crystal Castles took that genre forward in one great lead into the 3rd dimension.
"Get the Gems Bentley Bear!" is your only instruction you get and it's the only one you need. It's the standard PacMan gameplay; you just have to collect the gems that litter the ground. Instead of ghosts here you are chased by all manner of things more often than not of a vegetable (as opposed to animal) origin. The screenshots here of the first two levels have you chased by trees and what looks like giant blueberries.
Where the gameplay differs the most from PacMan is in the tunnels. In PacMan one of your best escapes from the ghosts was to jump into a tunnel and reappear on the other side of the screen. The ghosts couldn't follow you in there. The same applies with crystal castles but this being a solid 3D world there is no magic reappearing at the other side of the screen. These tunnels are more complex, often involving corners and when you can't see Bently Bear when he's in one it's often rather difficult getting him out again.
Crystal Castles was half way between PacMan and the platform games of the future. It's fast, it's great fun, so if you missed it in the arcades the first time around go check it out now.
Jakey 09 May '03
KLOV - Crystal Castles page - The Killer List of Video Games has detailed info on many classic games.
Wikipedia's Crystal Castles page - Lots of great information.