As described by the press release:
Creatures models real biological systems inside your computer. They come complete with their own biochemistry, brains, digital DNA, and an environment in which to live.
None of the behavior you see has been specifically programmed. The Creatures make their own choices, and learn from their mistakes. You guide them through their lives, helping them through the bad patches and enjoying the good times. When they become adults, your Creatures can mate, and their children have their own unique genetic material.
The possibilities are boundless. Everything from their poses to the individual chemical reactions inside their bloodstream are genetically specified. Who knows? A tenth generation creature could possibly be considerably more intelligent than those you start with.
Your Creatures live in their own world, called Albia. Albia is a huge world, it contains many exciting places to visit, and many dangers. The Creatures you hatch are from the species known as Norns. Norns are a friendly, curious, social species; eager to learn and experience life to the fullest. Grendels live in the trees, with different genetic material; they are violent, steal food and carry diseases.
Above all, Creatures is for your enjoyment. You can become as involved as you want, the ultimate aim being to breed Norns through multiple generations. You may be the parent of the first super intelligent Norn!
Creatures was a favorite "fishbowl"-type game much like Little Computer People and Seaman. It's nice to see the series revived.