There are two words made to describe this game: Cult. Classic.
Treasure sure knew what they were doing in back in the day. They managed to predate Metal Slug by several years, plus make a similarly fun and detailed game in the much inferior Genesis hardware. They later did it again, this time with beat'em'ups in Guardian Heroes. And every time, their games were acclaimed by critics and the selected few who played them over and over again, then forgotten and overshadowed by more popular clones, most of the time not as good.
But we're talking about Gunstar Heroes on the Wii here. It's actually a pretty simple review. If you played or want to play Metal Slug Antology and 6 MS games don't seem enough to you, you MUST play Gunstar Heroes. Then again, if you're not in the least interested about Metal Slug, you MUST play Gunstar Heroes... and then you'll probably rush out and buy Metal Slug Antology just to have a viable alternative in the same vein.
Yes, it's that good. It's a very short game, yet I've played it over and over, pretty much a couple of run throughs a year. In Gunstar Heroes, every one of the four main stages is a game on its own. From the first, straightforward side scrolling run'n'gun, which has heavily influenced, as I keep mentioning, the Metal Slug saga, to the fourth one, a tabletop game in which you do grapple moves to throw a dice and decide what challenge comes next.
Then there's the control scheme. You get to choose if you want to stop to aim your weapon or move while you shoot, you get to choose your starting weapon and one of two characters. From there, the options are just endless, since any other weapon you grab along the way will blend with the current one to produce new effects. In a way reminiscent of space shooters, you might even downgrade your weapon's power if you choose the wrong combination.
But don't worry, because you're sure to come back after you've finished the game once to purposefully test new weapon combinations and gameplay styles. Granted, the shoot+move with a homing+laser combo is the killer app of the game, but after a while, each stage becomes its own thing, like playing a song, and it will be performance and variables what will get you to replay this game for as long as you keep your Wii.
So here's to detail, to developers who stick to their good ideas despite moderate commercial success, to a wise choice of a game to re-release and to all of us who get to play this old, rare gem once again.