This game might be a bit redundant - seven of the games in the Metal Slug series were already released on the Wii in collective form as Metal Slug Anthology. However, none of the games on that disc allow for classic controller use, so if you desperately want to use it, then you have no choice but to buy it on VC. The Anthology also had some weird control choices, like flicking the Wii remote up to throw grenades. That's gone here.
Metal Slug is quite a bit like Konami's Contra series: you play as Marco Rossi and must run and gun down a truckload of all sorts of weird and wacky enemies. Get hit once and you're dead. The difficulty is obviously quite high as well because of this. Weapons include machine guns, grenades, flamethrowers and more pretty realistic stuff. You also take control of vehicles like tanks and have the option of rescuing prisoners for extra points.
The main enemies you will face are soldiers. These guys are great, and can be seen doing all sorts of stuff before you burst onto the scene, like sitting around a campfire eating, talking with each other, or even sleeping. Most of this is thanks to the excellent (and we really mean excellent) sprite-work. The game easily has some of the best 2D graphics ever made, as everything moves incredibly fluidly. Screen-sized bosses have no trouble looking smooth, and tons of stuff in the background, such as houses and boats, explodes and breaks down all the time. Music-wise there's nothing excellent to speak of, but it does get the point across, as it's fast-paced and quite lively.
The game is highly regarded among tons of gamers, so you can honestly do no wrong in downloading this title. This will probably be the best Neo Geo game on VC for quite a while.