The Metal Slug series may be one of the most revered “Run N' Gun” games since Contra or Gunstar Heroes, and luckily, each new entry in the series keeps up to the high standard set by the previous game. These type of games are 2D, side-scrolling, action-heavy, challenging, and arguably very old-school. Metal Slug 4 and 5 are no different.

These are arcade perfect versions of their respective titles, and even go so far as to include Xbox Live scoreboards to see how well you stack up against people all over the world, not just your local arcade. They feel great with a controller, and the addition of rumble adds even more to the experience. And, perhaps most importantly, you won't need an enormous pocketful of quarters in order to get to the end of the game.

Actually, conversely, that's the only real discrepancy as far as arcade conversion goes: you don't run out of continues, ever. Sure, you can choose to let the timer tick down to zero, but there's nothing stopping you from trucking on to the finish. Strangely, while you can't change the infinite continues, you can change the number of lives you get per continue. Luckily, the game keeps track of all sorts of stats, including the number of continues you used in a play-through. Still, the lack of an option to turn off infinite continues may not sit well with purists.

Nonetheless, the game is a blast. Each level is distinct and interesting, and some of the highlights include a river ride through a jungle, a high speed highway chase, a grungy, zombie-filled town, and a rundown old factory. Each level is loaded with civilians to rescue - most of which are long-bearded hippies, for whatever reason. They'll give you a present for saving them from the enemy, be it a bundle of points or a better weapon.

The game can be quite challenging at times because, except for your first life on a new continue, you start with a rather underpowered pistol. It's great for hitting soldiers, but is absolutely terrible at taking down anything with a bit of armor on it, whether that be tanks, helicopters, mobile suits, or the terrifyingly large bosses. Luckily, there are other weapons to aid you. One of the more common and consistently useful is the heavy machine gun, which fires off a rapid stream of damaging bullets, and is perhaps the only gun that shoots diagonally. There's the shotgun, which doesn't have a very long range but is almost guaranteed to take out any near targets with one blast. Or you could grab a bazooka and fire off some rockets. One of the stranger firearms launches rockets on wheels, which plop to the ground and zip along very quickly until they hit something. All of the special weapons have limited ammo, as opposed to the handgun, and your character also carries ten bombs that can be tossed like grenades.

What do have high powered, unlimited ammo, however, are the sweet tanks and other vehicles that you can hop in. Just about everything is equipped with a heavy machine gun or sometimes two, and can sustain fire in any direction. Additionally, being armored, the vehicles can take much more damage than your character, who dies from a single hit. Taking advantage of the big equipment and using it effectively can be the difference between a breezy mission or a very difficult one.

Metal Slug 4 features some cute little surprises. Since the nearly nonexistent storyline revolves around capturing a deadly virus from evil hands, a few scientists pop up from time to time to use this weapon against you. Getting hit with a dart of the vaccine might cause your character to turn into a zombie itself, lumbering and slow and not able to jump high or far at all. The zombie isn't completely underpowered, actually, as using a bomb results in an incredibly destructive wave attack. In addition to the zombie, I've also had some experience in turning into a monkey – a monkey in a diaper, no less. The ape gets machine guns and can jump surprisingly high, but walks slower otherwise. These little transformations, while nothing earth-shattering, keep the game fresh and fun.

While Metal Slug 5 doesn't offer the transformations of the former title, it is considerably more versatile in other ways. You'll take to the skies to take down a dangerous aircraft – first in a very capable plane of your own but you'll find that your character can glide along just as well without it, if you lose it. You'll also take a bit of an underwater dive, streaming through with a cool little submarine. There are generally just more modes of transportation in Metal Slug 5 on the whole, from the aforementioned to motorcycles and a number of tanks and even a jazzy mobile suit.

The game features absolutely astounding 2D graphics. The animation in these games are unparalleled, not only on a side-scrolling shooter level but compared to 2D games overall. Everything from the run animation to bullets hitting walls to blood spurting from hit soldiers to the tread on the tanks is incredibly smooth and stylish, and the attention to detail is impeccable. It doesn't hurt that each level is wonderfully designed and has lots of exciting things to look at, and the character art is great.

Sound is not bad, if not as impressive. There are some good background tracks here, but the sound effects are the main focus here, and they're more than adequate. Gunfire, explosions, engines, yelps of pain, and all the other noises of war are right here and feel right at home.

Metal Slug 4 & Metal Slug 5 are fantastic games. Although they're not terribly new or thought-provoking, they are very, very fun to play. Even though each game can be finished in less than two hours with infinite continues and a little skill, they practically insist on replaying them to sharpen your skills or just another play with a friend in co-op. If you feel like sprucing up a library of games sorely lacking in 2D action, look no further.

Gameplay: 8.0
Not super innovative, but not generic in the least. The controls are sharp, the weapons exciting, the level design good, the vehicles very cool, and everything moves along really smoothly.

Graphics: 8.0
This features, frankly, some of the best 2D animation around, as well as being generally well designed.

Sound: 7.0
The background music is fine and the sound effects work. No complaints here, but nothing remarkable, either.

Difficulty: Hard
Granted, the infinite continues makes finishing the game fairly simple, but actually doing well on each mission is something completely different. Skill, memorization, and a little intuition are needed if you want to impress anyone or improve your score.

Concept: 7.0
Neither of these games are a big step up from, say, Metal Slug 3, but there aren't many developers left making games like Metal Slug 3, either.

Multiplayer: 8.0
Aside from the leaderboards which may or may not intrigue you, the game offers a co-op mode which is simply a great deal of fun with a good friend.

Overall: 8.0
Metal Slug 4 & Metal Slug 5 is, without a doubt, a great addition to any gamers library. There just aren't many games like this being produced, and thankfully the Metal Slug series continues to offer astounding quality. Plus, you get two games here, for less than the price of a full-priced title – it's an offer that shouldn't be refused!