Okay, so the name kind of gives the game away. It's a tank game. Of course, this being the '90s nobody would dare release a simple Battlezone clone. Nope, what we get with M4 is a complicated Battlezone clone - lots of your obligatory solid 3D vectors, a fair bit of bolt-on strategy, and a rather massive dollop of shooting. The programmers have obviously realised that tank sims are normally boring as hell, so they've plumped here for an odd sort of halfway-house between a shoot-'em-up and a strategy thang.
So how well does it work? Well, just fine for the most part, though you do get a feeling of compromise. Each time I've played it I've found myself neglecting the strategy elements after precious few minutes, and getting down to some good old-fashioned tank bashing instead. It's not that the strategy elements are badly done particularly, but they do come across as a bit of an afterthought, stuck in there to make up for the significant shortcomings in the action department.
Still, I shouldn't whinge too much. For the money it certainly offers a sizeable amount of playing time, and I do enjoy playing it in a half-hearted sort of a way, though I'd still choose Battlezone any day of the week.