Bonanza Bros was the first Mega Drive game I ever played. It was the reason I was interested in the machine in the first place. Today I would put it up there with Quackshot and ToeJam & Earl as one of the handful of games that for me makes that machine so exciting. (I appreciate Gunstar Heroes belongs on this list too, but I had temporarily moved on from video games by the time that came out and I had to discover it much later.)
Even now, Bonanza Bros sums up what made 16-bit gaming so astonishing. On the surface, this is pretty simple stuff. You play as a robber - or two robbers in co-op - who break into various types of buildings, race around nabbing the stuff you're after, fighting off guards and then making it to the roof where a sort of airship allows you to escape. It's a pretty basic thing to play - I think the first time my friend plugged it into his Mega Drive he completed it in one sitting.
But that wasn't the full story - and the game mechanics not being the full story was what 16-bit gaming was all about. Games suddenly had time for incidental details. Sonic tapped his foot if you left him long enough, the kids in Mystical Ninja put their heads through funny hole-riddled statues for no reason. And in Bonanza Bros? Bonanza Bros was filled with incidental detailing.