The extremely popular Metal Slug is all set to appear on the PSP. It has been 10 years since the initial appearance of the original game and to commemorate the occassion, SNK is coming out with a special collection for the PSP. The Metal Slug Collection will include six games all together - the original Metal Slug, of course, plus Metal Slugs 2, 3, 4 and 5 and Metal Slug X. According to SNK, you can expect "perfect translations" of the arcade classic, and a Wi-Fi two player mode.

The game involves you playing a commando who rains "metal slugs" on the baddies in order to wipe them out. It lets the player control tanks and planes through the different missions. The basics though remain the same, they involve the player firing at will with different guns and killing all the bad guys (which unless you are playing in multi-player mode means everyone in sight).
Source: Eurogamer.net