Currently scheduled for release on the PlayStation 2 and Xbox in North America next month, SNK's Metal Slug 4 & 5 combo pack promises to be a real treat for fans of the aging side-scrolling shooter series. The compilation not only boasts excellent versions of the original Metal Slug 4 and Metal Slug 5 games, but also adds new playable characters and four levels of difficulty to the mix. The default difficulty setting is normal, which is slightly easier than the original arcade or "MVS" (NeoGeo's Multi-Video System) setting. At either end of the scale, you'll also find easy and hard settings.

　　It's you against everyone else, and your enemies aren't shy about attacking in numbers.

　　If you're not familiar with the Metal Slug series, then all you really need to know is that each of the games sees you assuming the role of a badass Metal Slug team member charged with single-handedly (or with the help of one other team member, if you're playing co-op with a friend) saving the world from an army of bad guys by running from left to right and killing every last one of them. You typically start out armed only with a pistol, a knife, and a handful of grenades, but you'll find that there's never a shortage of more-powerful weapons to pick up. There's also never a shortage of well-armed enemies looking to end your mission. And while they're mostly ineffective individually, the large numbers they attack in make them a force to be reckoned with.

　　The fact is, these games were originally designed to relieve arcade-goers of however many coins they were carrying. So, unless you have Metal Slug skills that border on being superhuman, you can expect to die...a lot. You don't have a health bar, you're more vulnerable to attacks than any of your enemies, and the moves at your disposal are extremely limited by today's standards. However, SNK has seen fit to make an infinite number of credits available in the home versions of both games from the outset, which you'll most likely love or hate according to what you're hoping to get out of them. If you're looking for games that take you back through time to an era when games were generally much more challenging than they are today, for example, then you'll have to be strong-willed enough to limit your attempts to a certain number of credits. If you don't, then you'll almost certainly be able to complete both games (11 missions total) in a little more than two hours the first time you play.

　　Metal Slug 5 features 29 different items for you to collect as you play through its five missions.

　　Since the Metal Slug games are so short, it's fortunate that you'll almost certainly want to beat them more than once, regardless of how you choose to approach the infinite credits system. You can try to beat the game using fewer credits than you did the last time, for one thing, or perhaps you can try to beat your high score, complete the game in a shorter time, or just explore the alternate routes that are a feature of certain missions. Metal Slug 5 also boasts an additional replay incentive in the form of 29 collectible items that you'll have an opportunity to collect each time you play. We're not sure it's even possible to collect all of them on a single run because of the alternate routes. In fact, after our first play-through, we were still missing 15 of them.

　　It's not like hunting around for items is a priority during a game of Metal Slug, though, because you'll actually be lucky if you have time to look for them at all. One thing you will want to look out for, however, are vehicles that you can jump into and use. You'll find plenty of land-based vehicles, such as tanks, trucks, cars, and mechs, that you can use against your enemies, as well as an airplane and a submarine, when they're needed. Unlike you, vehicles in Metal Slug are able to sustain multiple attacks before they're destroyed, at which point you'll have to manually jump out of them. Jumping out of an about-to-explode vehicle in the air or underwater sounds like a terrible idea, of course, but you'll find that Metal Slug team members are typically outfitted with jetpacks and underwater breathing apparatuses on missions that might require them.

　　The main differences between Metal Slug 4 and Metal Slug 5, incidentally, are that the earlier game is longer and arguably more difficult, while its sequel features more-impressive weapons, a little more jumping between platforms, and the ability to slide along the ground from a crouched position. These differences aside, the 11 missions included in this compilation could quite easily be taken from the same game, which is no bad thing given that they're as enjoyable today as they were when they debuted in arcades. In fact, you could argue that the versions of Metal Slug 4 and Metal Slug 5 we've been playing are actually better than the originals, simply because we've yet to experience any of the noticeable slowdown that fans of the series might remember from earlier incarnations.

　　The Vulcan fix option is available in both games, if you don't have some objection to using it.

　　Another feature of the Metal Slug games that fans might be aware of is the "Vulcan fix" option, which lets you lock a number of weapons (including most of those on vehicles) at a certain firing trajectory while you continue to move your character. This option wasn't a feature of the original arcade games and, as such, it's often snubbed by Metal Slug purists who feel that using it would be tantamount to cheating. The versions of Metal Slug 4 and Metal Slug 5 included in this compilation are clearly aimed at veterans and newcomers alike, so it's no surprise the Vulcan fix option is available on both games' menu screens.

　　Although we've only had access to the PS2 version of the Metal Slug 4 & 5 compilation to date, an Xbox compilation is currently scheduled for release around the same time. We expect the differences between the two versions to be minimal, although the Xbox version will benefit from the inclusion of Xbox Live leaderboards. Expect a full review of Metal Slug 4 & 5 as its release date closes in.