Yes the products are outdated and I don't see them getting a facelift any time soon - Dark GDK 2.0 is supposed to be the updated and less buggy version, but we've not heard anything for months from Mistrel, so I don't know if it's still being developed.
But that doesn't stop Dark GDK 1.0 being useful, it's still powerful and still functional. If you prefer it to other engines out there, I don't see any reason to not use it, despite it being out of date. I am using DGDK.NET and I know some folks still use it and likewise for DGDK (isn't Fallout using it for Carnage?).
Regardless, there's decent alternatives out there. Ogre and Irrlicht being the popular 2. XNA is another choice. I'd say they're more complicated than Dark GDK, but aren't too difficult to get to grips with, Irrlicht probably being the quickest to learn.
I think Dark GDK has an advantage because if you know Dark Basic Pro, there's a lot you already know - it's just taking the same commands & features and using them inside of a different language or in the case of .NET, learning how to use OOP versions of them.