Formed by a few former Human staff in 2001 Sandlot has since carved itself a niche as developer of games which include a large variety of scale, and messy explosions. Their games typically feature a small number of unique stages, but a large variety of events set on those stages.
In the Earth Defense Force series players control a human character under assault from an assortment of alien invaders: from giant ants and spiders, to classic sci-fi inspired UFOs. Stages are open, the goals being mostly nothing more complex than 'survive', or 'kill them all', but the large variety of weapons to be collected, and the range of freedom in reaching those goals, being the main points of interest. Also the fact that all the architecture is destructable ;)
In their mecha-themed games that destructibility, and general structure, is also present. In fact you get the sense that each engine is built on the one previous. while also controlled from a human point of view their main weapon is the mecha they control. Typically this is a complex operation, with separate buttons needed to send commands to independent move robots' separate limbs. Coordinating movement and attack is particularly satisfying, and immersing.