I use it's nearest competitor, Blitz3D (
www.blitzbasic.com) Check out my game Flamewar! a couple threads away to see something I've done with it. Long story short, the main difference between the two products is reflected in the development philosophies of their respective creators: the people who do DB are all about packing in the latest bleeding edge features as quickly as possible, while Blitz is built in a more paced way to focus on a well-designed language and stable features. As a result, DB has snazzy effects like shaders, but is a horrible language and is terribly bug-ridden. Conversely, Blitz is slightly behind the times in technology (eg. it's based on DirectX 7) but is a much better language and has pretty much zero bugs. I think it's clear which way I prefer.
Incidentally, the new version of Blitz, BlitzMax, will have a 3D module soon, and that'll use OpenGL and run on Windows, Macs, and Linux. It's kinda silly to base purchasing decisions on predicting the future, but Blitz Research has a great track record so it's something to keep in mind.