Digger is quite a simple game. Basically you are a little digger like thing that appears to be alive. To progress to the next level you have to collect all the emeralds shown on the current map, which you can do by tunneling throughout the map.
The enemies on the map are the strange Nobbin creatures that if they touch you, you die. When Nobbin rub together they create Hobbins which can tunnel through the map like yourself and also kill you at a touch. You do have several ways to kill them though.
The first weapon you have available is you gun. Apparently this digger is equipped for warfare. Yes, just a click of F1 and you'll fire a asterix looking fireball that will kill the first enemy it hits, or else hit harmlessly into the dirt (the Nobbins and Hobbins are quite good at dodging).
Another good way to get them is by dropping the Gold bags on them. It crushes the enemy and leaves a pile of debris which if you go over gives you points! The same debris is left by dropping a gold bag at least 2 spaces, but beware as they can crush you too.
Finally, the pièce de résistance is the "Bonus", i.e. cherries. Reminiscent of Pac-Man, getting the cherries makes the screen flashy and enables you to gobble up the Nobbins and Hobbins in your digger mouth, Mwahahah!
There are pretty much two ways to play Digger, for points or for levels. The best way to get points is to lure the Nobbins around a single track for as long as possible, waiting for your gun to recharge and taking them out as they respawn. For levels you just need to run round like mad, getting as many gems as possible and killing Nobbins as you go. Careful with this approach though, as when you have multiple tracks the Nobbins are more likely to meet and fuse to create Hobbins.
A classic game, simple yet addictive. If you want to play it yourself, you can find a remade version online here, or even download it to your PC with a level editor and more from here! Note: to use the downloadable version you'll need a DOS emulator like DOSbox, which is easier to use with a front end, I use D-Fend Reloaded. Another thing I will note is that a HD Digger version has been released for the PS3, shown above, with new graphics and new features and also includes the original game, available from the PS3 marketplace.