Metal Slug 3
I just got this for the PS2 the other week and I can't put it down. It only takes about an hour to finish, but it's pure arcade mayhem all the way.
Pure side-scrolling shoot-em-up, frantic non-stop mayhem, classic arcade action. The way games used to be :-D
I'm hoping to get 4 & 5 for Xmas :-D