Soya 3D

You can build games with a animated characters, landscape, and interesting things (houses, power ups, enemies, etc) with only a few hundred lines of Python code. There's an example which does this with less than 100 lines (just running around and jumping).

There's also lots of special effects you can use by just enabling it and giving a few parameters. Two different network engines are available for it, Tempeh and Tofu, which let you build multiplayer online games really easily.

Soya has exporters/importers from many 3d modeling applications such as Blender (also free).

It's free software for Linux, MacOSX, and Windows.

The Soya 3D website at http://www.soya3d.org/ has tutorials, screenshots, artwork and models you can reuse, and downloads.