Super Mario Land
This series was a great set of Super Mario games released on the Gameboy but by the third game, the series with Mario had been abolished and Nintendo started making Wario Land games instead. But here is some information about the first three games in that series (I never bought Wario Land 2 or 3, and Wario Land 4 isn't quite a Gameboy game.)
Super Mario Land
In this game, Mario had to save Princess Dasiy from the evil alien Tatanga. For some reason, the enemies were actually Mario series enemies with odd names, and the lands were strangely based on odd themes, sometimes real world areas!
The first area is an Egypt themed world, with sphinxes, piranha plants and a boss which was a sphinx which jumped up and down while breathing fire.
The second world was a water planet. I think it was a planet because of the spaceship at the start, and at first was just jumping across platforms set in a huge ocean. The final level here had you controlling Mario in a submarine and shooting enemies with torpedoes!
The third area was based on Easter Island, with those weird stone head statues. It also had bouncing boulders and tarantulas, which on my last count, have nothing to do with Easter Island!
The final world was set in the sky. The first level was just jumping around above the clouds, and the second area was like a maze with fire breathing snakes! The final area had Mario in a plane shooting down enemy birds and planes! You then had to fight a cloud boss before shooting the final boss who appeared afterwards in his spaceship!
Super Mario Land 2
This time, Mario was claiming back his island and castle from Wario, who had invaded the placed with an army of monsters! Wario made his first appearance here, as the villain!
The areas were odd to say the least. From a giant tree with killer insects, to an underwater area with levels set in a submarine then a whale, a haunted house filled with boos, an area where Mario explores a house while bug size and fights a rat, a world inside a giant Mario. This game had it all. Plus, it had a world actually set in space!
Of course, you got to beat up traditional enemies and invade the castle at the end.
Wario Land, Super Mario Land 3
This game was the first to star Wario, who had set out to claim a giant statue of Princess Peach which was captured by the Sugar Pirates, led by Captain Syrup! This game had a neat intro of the ship being smashed to pieces by Wario, and also secret levels/plus a secret world!
The areas were named after things in a kitchen, hence the place was called Kitchen Island! Such examples were Mount Teapot, Stove Canyon, Parsley Woods, the Fork Tree and Syrup Castle.
I remember this game just for the fact I always got killed on a level where a cloud of darkness was following Wario lined with deadly spikes! Ah, Stove Canyon, best music ever and the most annoying first level