Prey is another one of their titles. It's still selling pretty good actually, and is one of the things that's publicly known- they've done a handful of other projects that their name didn't get put on it because they were the subcontractor on the project.
Couple this with keeping a good control on the good money they got from Terminal Velocity, Duke, and Shadow Warrior, they've been able to keep going all this time. It remains to be seen if DNF is going to be worth the wait we've had- but some people that've seen the current "attempt" at it that may well be on it's way to Gold status have been at least mildly impressed. We'll see- I'm still sitting on the fence on this one. If I can get them to give me the time of day on a discussion of a Linux/MacOS version port and see it for myself, I'll change that position.
But Prey was made by Human head, not 3DR. The last game they actually developed was Shadow warrior, over a decade ago. Its amazing how they can live (rather lavishly) from dos era yesterhits.