And they are taking on more. Starship Troopers later this year as both a non-D20 RPG and as a minis game. It's supposedly really hard to make money off of licensed properties, I don't know how they do it. And they keep up a decent release schedule.
While their written material is top-notch, on the graphics side Mongoose errs on the side of speed rather than quality. There are very few custom graphics and pictures used in their books and when they are used they often are crude-looking (see the Worker-caste symbols in the Minbari book). Also some of their screencaps, which account for most of the internal art, is a bit grainy and blurry.
On a plus side they often buy graphics from the people who do fan-cgi. I have seen quite a few pics from various sites ending up as pictures in the books.
Also, the B5 game uses a lot of dedicated freelancers like August Hahn and Bruce Graw. Though I know August does other d20 work and Bruce is now the miniatures guy for Starship Troopers, their focus seemed to be Babylon 5 for the last 8 months.
In short, Mongoose is very dedicated to getting products out the door quickly - even if the visual presentation suffers a bit because of it. Interestingly enough, even though their books do have some errors, they don't seem as bad as some other products which are much slower released...
I love deadlines - I love the whooshing noise they make as they go by
- The late Douglas Adams