Me and Apex discussed about this yesterday.
You can make any kind of game with DGDK. Of course it wouldn't be the state-of-the-art in graphics, performance, etc. But you can make any genre of games with it, even create your own new genre.
The great problem is: people tend to forget the ammount of work necessary. Imagine an MMO RPG (or any MMO game). It already says that is online, and MASSIVE. It's not only making a "cute" game, but you must think about the server first, have a good knowledge of TCP/UPD transmissions and a lot more. DGDK's Multiplayer is, as far as I know, a wrapper to DirectPlay, which is DEAD, and would never support a MMO.
One piece of advice. If this is your first time with DGDK, and even more important if is your first game making attempt, start with something simple but fun, a game that you are pretty sure you can complete: finish, polish and release.It might not be the next "The Sims" or "Mario" (in terms of financial success), but it is something you can look at and say: "I DID IT!"
I'm not discouraging anyone, nor am I saying no one is capable of doing great games (plenty of great ones in WIP forum). It's just that it's too sad seeing a lot of new faces around (after DGDK was released for free), people wanting to do MMO's and FPS's, but cannot (or won't try) to understand the included Samples, like a simple space invaders. Even a lot more wanting to make games without knowing how to make simple operations in C++. I am saying this because 9 years ago, I was one of these kind of people, but
I really only learned something when I forgot about it and started learning how to program simple things. Then, two years later I finished my first game: Snakes (Done in Delphi with DelphiX, if I'm not mistaken). Idiot? Maybe, but fully finished.
@mcwell: My long post is not destined to you, don't worry. And welcome to DarkGDK forum. About your question, you know the answer already
Regards,
Thiago