First off, I'll say that the jaggy, messy-looking screenshots released before do not reflect the (not even) final game. In fact, the game looks great, with all of Metal Slug's signature animations intact. The game is controlled with d-pad and buttons (I didn't even think to mess with the stylus) with a progress map on the lower screen. There are six selectable characters: Marco, Eri, Ralf, Clark, Fio, and Tarma. Each comes with a different default weapon; Marco's, for example, was a lightning gun. The levels are rife with bearded hostages, as is the custom for this series, and lots of enemies to be shot and knifed.
Unfortunately, I can't provide detailed impressions of multiple levels, because despite my best efforts I died early on in each level. I kept trying, though. There seems to be a mission mode that divides the game into shorter missions; however, since all the interface was in Japanese, I can't be sure. Again, not dying frequently would have helped here.