If you enjoy games like Metal Slug and Contra, you'll love The Chaos Engine.
This is a Bitmaps Brothers game, so the look and feel is awesome.
The game mechanics is a mix between Gauntlet and Ikari Warriors, yet I like it more than I ever liked those other two and for a good reason. It's better.
There are always enough baddies to keep you on the edge of your seat, but not enough to make you feel overwhelmed. Some look crazy but they're all cool and each world sports its own set of them, so you only get the giant frogs on the first world, the black blobs on the second one, the walking hands on the next one and so on.
While there are no secret levels, there are several ways of entering, exiting and going through some levels. That makes the game very replayable. When you take one route, the other is blocked and the only way to know what's over there is to play again. Each route is filled with goodies, so whatever you choose, you're not going to regret it.
Having six characters to mix and match also makes the game very replayable. And your sidekick, while not always useful (read below), at least doesn't get in the way. If he's left behind, he'll be teleported to the current screen, and you can always pass through him.
The music is good, but there's only one background track for sixteen levels. Why they couldn't hire some guy to add more music? Same thing with the sound effects. Why so few of them?
Eight-way scrolling games have never been a favorite genre of mine, but the few I've played at least let the player shoot and move at the same time. On this game, the player can do one thing or another, but not both. It's no deal breaker, but it's not the best way to play neither.
The eight-way scrolling also makes your CPU-controlled sidekick very unreliable. If there's no angle for him to shoot, he just stand there until the monster reach a place he can shoot at or he moves accidentally to a better position when he follows you. This limitation makes some levels harder than they already are.
If you're one of the few who are still playing on a console, there's one more thing. Instead of getting a password after every level, you get one every other level. That means that dying on even-numbered levels forces you to replay not one but two levels. That's not fun.
The Bottom Line
Like Contra, The Chaos Engine is hard but not unbeatable, and like Metal Slug, it offers plenty of reasons to play it again and again and again.