I've been interested in making a mission for this game since the Foundry tools initially entered public beta, but I don't know how difficult they are to work with. Could someone give me a bit of perspective on this? I can use Valve's Hammer world editor tool competently. How does it compare to that?

Once you play around with the toolset, you will be able to do a lot of things easily.

I recommend watching the terrific tutorial videos here:

http://www.startrekonline.com/foundry_video

There's certainly a curve, but with a bit of practice it works out fine. Check out those tutorial vids as posted above.

The easy things you can do with it are easy to do. Interesting things . . . not so much. If you don't want to push the envelope a lot, you should be running away with it in no time.

and if you do want to push the envelope a lot, other then one lined responses while @ work..... you will not be heard from for weeks (months)

Check out the tutorials at http://www.starbaseugc.com, as well. They are extremely helpful.