Wario shares many qualities with his smaller cousin while adding his own dastardly personality to the mix.
Wario jumps and runs through side scrolling levels much like his hapless counterpart. Though, while Mario is small and spry, Wario is huge in lumbering. Mario's typical attack of jumping on enemies heads is retained but supplemented by an ability to bash enemies with his shoulder and add additional height to jumps by holding the up button while jumping. The downside of these new abilities is it seems to come at the expense of being able to hold down a button to run, which can be frustrating at times. He feels a bit sluggish at first but as you get used to him--and accept he is not Mario--the controls feel intuitive and responsive.
At the beginning of the game and after dying, Wario starts out wearing his ordinary safari-style pith helmet. This is equivalent to being big Mario in most games and that you start out in this state is an interesting change in the system. Wario can find three different hat upgrades all of which add special abilities which take a while to get used to but which prove very useful and even necessary at points to pick up certain items and get to some areas. If Wario is hurt while wearing either his standard hat or the upgrades he converts all the way down to small, hatless Wario, who is not only one step away from death but severely crippled by the lack of ability to bash things which his shoulder, leaving him w/ stomping and throwing as his sole means of dispatching enemies.
The object of the game is not only to beat the final boss, a woman pirate named Captain Syrup, who has control of some kind of crazy genie thing, but to do so after collecting the most coins and treasures possible. After Captain Syrup is defeated, Wario is awarded a house based on the income he collected throughout the game. His journey is not terribly difficult, populated mostly by weak enemies and some very light puzzle solving, but there are some challenging platforming elements and its fun enough to give you incentive to seek out and find bonus areas, which adds extended playability. Boss fights are varied and add just enough toughness to leave you satisfied while at no point really making you want to chuck your Game Boy into a wall. At first play feels quite linear--like a NES Mario Brothers game--but once you get off trying to collect treasures in coins, it takes on a more open world fee.
The presentation is overall quite good with detailed (for Game Boy) graphics and absolutely wonderful music with these humorous quacking basslines that compliment the cartoonish style excellently. Top to bottom, this is a well put together game which fans of Mario or platformers in general are sure to enjoy. The Wario series eventually went on to become many things this game is not but already this is many things that Mario isn't.