I have a pretty classic love-hate relationship with the Metal Slug series. Whenever I pick one up, I'm wowed by the hand-animated old-school graphics, the classic 2D gameplay leaves me transfixed with nostalgia, and I think the games are awesome.
Then the game slaps me around like an unpaid pimp and I have to put it down for a while.
In past Metal Slug games, such as the third one, I played the game as much for its lunatic sense of invention as I did for its rock-solid, unforgiving gameplay. Metal Slug is a sidescrolling arcade shooter of the Contra school, but it bears little resemblance to that game; instead, it's sprite-based gaming as animated by an obsessive-compulsive and his crew of sadists.
Every little part of the game, from the gunfire to the occasional giant death robot, has tons of animation and personality. Enemies struck by gunfire don't just fall over backwards; they jet blood like the lawn sprinkler in Hell, then collapse into a heap. When you die, you don't simply collapse; instead, you get to see one of a few dozen death animations, from gunshot wounds to bursting into flame and keeling over.
That last bit's helpful, because the Metal Slug games have always been about the pattern memorization. They're arcade quartermunchers, and as such, thrive on killing you without any notice or regret. You have to know what's coming in order to most effectively dodge and counter.
In Metal Slug 4 & 5, you're getting the two newest games in the series. One of them is good; the other's kind of bleh compared to past installments.
The mediocre one is Metal Slug 4, which features a new character, Nadia, but removes a surprising amount of the variety that makes Metal Slug worth playing. There isn't much in the way of different routes through each level, and the visuals aren't up to par with Metal Slug 3. The sprites are the same, yeah, but there isn't quite the same sense of relentless and inventive danger.
MS4 would be a great game if its immediate predecessor didn't exist, and it's still quite playable. The sad fact of the matter, though, is that once you've been transformed into a blood-puking demon zombie, as you were in MS3, it's hard to go back to shooting hordes of enemy soldiers.
Metal Slug 5 is a step back in the right direction. It starts off with a mad canoe ride down a jungle river, and before you know it, there are evil jungle warriors, toxic worms, ninjas, and a tank every time you turn around. It's a bit more newbie-friendly than past games have been, and it's a lot of fun.
When you drop the money on this, you're getting two arcade-style shooters that're entries in a famous and well-regarded series. It'd be a little more worthwhile if an arcade-perfect Metal Slug 3 had been included in the collection, but this is still a must-have for those of us who fondly remember our local arcade.