According to Tim Conkling, its designer, Corpsecraft is an RTS-Match 3 hybrid; but actually, the RTS-ish gameplay is closer to that of Rescue Rangers or Steam Brigade than it is to, say, Warcraft.
Each player has a base at opposite sides of the screen, and builds units (various types of zombies, for the most part) and dispatches them to attack the enemy. They stagger across the screen, fighting each other, the ultimate objective being to reach the enemy base and destroy it (over time, with repeated attacks). There are several different unit types (introduced over a number of levels in the soloplay game, so you may learn their characteristics more readily), each with different characteristics.
Unlike an RTS, you have no direct control over your units; they simply follow their programming. Instead, you play a match-3 game (at bottom center in the screenshot); each color corresponds to a resource (red = blood, white = flesh, yellow = scrap, blue = energy), and each type of unit requires a different mix of resources to produce. Selecting a group of three or more of one color scores points (more for larger groups), as in every match-3 game -- but these contribute not to your score, but to your stockpile of the matching resource. To the left of the match-3 area are icons for each of the unit types; you create one by clicking the corresponding icon.
Thus, gameplay is a matter of monitoring what's going on in the RTS area, determining what sorts of units you need to deal with events there, and matching three madly to generate as many resources, preferably of the type you need most at present, as quickly as possible.
In addition to the solo training game, Corpsecraft is playable by up to four people at once, and at least when I visited the server, it seemed that there was usually someone waiting for a game.
The graphics themselves are nicely and creepily Gorey-esque, and the cross-fertilization of genres is interesting -- but I wonder whether the whole is greater than the sum of its parts. Consider Puzzle Pirates, the 'casual' MMO from the same developer; in that game, you play puzzle games to perform tasks in the overarching MMO (pumping the bilges, firing the cannot, sailing the ship), so you need to enjoy playing puzzle games, and have a feeling of contributing to the collective efforts of your ship mates. Moreover, the palate and art approach is cheerfully 'casual' in nature. This works; in Corpsecraft, it's not clear to me than an audience that enjoys, say, Bejewelled will find the match-3 experience enhanced by a gothy metagame around it, nor that an RTS audience, or one that is attracted to the gothic, will want an interloping match-3 trope.
Still, it's an imaginative and well executed attempt to do something a little different.