Sorry for being unclear. By "like insect monsters" I meant the format rather than the subject-matter. If you want to do concept art, don't neglect environment either. However, the big, vague mood shots are not all that practical in production. Bottom line is, can a few 3d artists look at your concept and make the scene without constantly asking you what everything is? Try to be specific and try to keep in mind where game camera is (1st person? RTS-style camera?) and concept accordingly.
Here's a really good thread of concepts done for a single game: http://www.conceptart.org/forums/sho...d.php?t=118126
Note that there are mood shots and quick ideation sketches in the thread, but there are also more developed scenes, in-game-shot paintovers, concepts of single environment props, and linedrawings. If you can imagine yourself playing through the environment, and show gameplay consideration in your design, you'll win bonus points with game companies.