Non stop classic arcade quarter pumping action are exactly what you get with Metal Slug X.
Metal Slug is a side scrolling shooter where you have a random weapon from a pistol to machine gun or the rather questionable iron lizard, as well as grenades to toss at the non stop flow of soldiers zombies and aliens trying to take you down. You rescue shaggy p.o.w.(s) to recieve points or new weapons. You carry one weapon at a time, giving the game variety of how to scroll through these adventures.
Nothing is truly special about any of these games, simply they are fun, hillarious with cheeky humor and challenging to get as far as you can without dying. The PSX version adds a survival and timed mode through its 5 stages which lets you judge how good you are and master your talents to show that neo geo who's boss the next time you feel like a milkshake. Aside that, it simplifies the game with unlimited continues which I admit is much better then using my milk money but unless you truly want to challenge and frustrate yourself you will no doubt take this one down in an hour or two. A really good game to have inbetween your 50 hour adventures in Final Fantasy or Devouring Locusts in Gears. You could even play it everyday and really not get too tired of it. Awesome!