Not interested in those though, I'm more interested in the likes of A.B.Cop...
You'll know of Chase H.Q. the 1988 classic that saw you chasing down bad guys in a Porsche 928 Turbo. Well it seems that Sega wanted in on that action and came up with A.B.Cop - a game that takes the same premise and ramps up the speed and crazy by replacing the Porsche with a jet bike (eerily similar to the one in the open scene of the Star Trek reboot movie).
It also replaces 'Ralph, the Idaho Slasher' with an eight foot punk shooting fire and wielding an enormous mace... How to improve a classic - Sega style.
Pushing the boundaries of what could be a considered a 'Hidden Gem' is Alien vs Predator.
Capcom receive more requests to update this game than any of their other side scrolling beat-em-ups, so I guess I'm really stretching the definition... but I don't think enough people have played this excellent, gorgeous game so it's staying in.
It's also the only time that the human star of the original AvP comics appears anywhere outside that series, worth a mention on it's own, considering the size (and dubious quality) of the IP.
Lastly, another stunning side scrolling brawler - you'll be seeing a lot of these.
Armored Warriors has turned up a couple of times under other names, whatever you call it though, it's an absolute beauty of a game.
Here you're piloting a choice of 4 incredibly detailed Mechs against a whole bunch of enemy incredible detailed mechs on a series of incredibly detailed battlegrounds.
The USP of Armored Warriors comes when you destroy a bad guy and parts of his mech might litter the the battlefield - because you can pick them up and use them to upgrade your own unit. Arms, legs, integrated weapons and more are interchangeable - you find yourself picking on the toughest bad guy in a crowd just to get his sweet Drill Arm upon defeating him.
And just when you a game can't get more awesome, there's a tag team move if you're in multiplayer too.