Master of Defense (download free trial here) is a quirky strategy game published by BigFish Studios which breaks the mold a bit on casual games. The first difference is that it's a fast-paced, real time strategy game involving a fantasy world of magic and monsters - no Tetris clones here. The second difference is that it requires a 3D graphics card, which is pretty rare for this category, although the general system requirements are still pretty lightweight, so it shouldn't be a big problem.
So why is it considered a casual game? Well, it's a simple game which requires only a mouse and no instruction book - you must purchase, place and upgrade a series of different defense towers which you use to repel a wave of attacks by different types of air and ground monsters. But that simple premise (only 5 types of towers or defenses and the monsters move along a set path) involves a fair amount of strategy as you begin to understand how they work together, and how to allocate your points to enhance them, so the gameplay is deeper than what first appears.
I'm not 100% sure there is enough gameplay here to warrant purchasing the game, and I'm not sure it will appeal to the bulk of today's usual casual game buyers, but it's a creative attempt to expand the types of games and buyers for this sector, so I have to applaud it, especially since it was developed by a small indie studio called Voodoo Dimention.
Verdict: Creative effort for a niche audience - worth a try - Get it here