METAL SLUG X / SNK / Arcade
Metal Slug X is basically just a revamped version of Metal Slug 2, but it has quite a few enhancements and is very much deserving of a look.
It actually uses the engine from Metal Slug 3, and the primary advantage of the game is that the slowdown that occurred in Metal Slug 2 when many characters were on-screen is now gone. The game remains fluid and at a consistent frame rate throughout. There are some aesthetic tweaks as well - the music has been enhanced (and generally improved in sound quality), the stages have some new background features and there's a more satisfying ending than in previous.
The levels also feature a greater number of enemies, as well as more heavy weaponry. Enemies also have been switched around in some cases, and the weapons have more destructive power and more impressive visual effects when fired. There are also some new weapons exclusive to this game.
My only nitpick with this one is that, while they were out and about revising Metal Slug 2, why not add the ability to shoot diagonally? It's been the greatest detriment of the series thus far and this seemed the perfect opportunity to incorporate it, but you still can only shoot straight upwards and can only shoot straight downwards while jumping. It's a bit stiff and cumbersome.
That's just one small and forgivable flaw though, in the midst of a really great run-and-gun with an excellent presentation and a bizarre sense of humor. This is good, solid, and reliable brainless shooting fun for one or two players.
* Gameplay Video