Its hard to actually consider a game absolutely perfect to play, but Nintendo had somehow managed to accomplish that with Wario Land 3. I don't know whether its the large, open game levels or the perfect way that puzzles and different challenges leading to different treasure chests were designed in the game.
I will attempt to make this review as spoiler-free as humanely possible, although I actually played this game to a 100% completion and enjoyed it all the way.
Graphics - 4.5/5
For the GBC era, the graphics are perfect. Areas look detailed, the colour palette is used really well. Wario looks far better than he did in WL2 and furthermore, everything looks clear and concise in terms of how the game actually looks.
If theres one small criticism about the graphics, its that you can tell the game was made using a tileset, although for a cartoony game which manages to make even tileset generated levels look fun, detailed and even somewhat realistic, you won't really give a crap.
Plot - 4.5/5
The plot at first seems very basic. Wario is flying an airplane on a cloudless sunny day when it crashes. He then encounters a cave with a Music Box, plays it and then gets whisked into the world inside this jukebox. A mysterious figure at a nearby temple then agrees that if he retrieves the 5 Music Boxes scattered across the world, he will be sent back to his own world.
Seems basic enough, but there are a few plot twists particularly towards the end of the story, which I will not spoil here, and will explain everything. Nonetheless, the plot suits the game, although the Magical Music Box world seems quite unreasonable, but then again, this is a Wario game. Who said it had to be in any way realistic?
Gameplay - 5/5
The gameplay revolves around the fact that Wario cannot die. He can be temporarily hurt or have his condition changed (e.g. set on fire, stung to the point where he floats, fattened, frozen, turned into a snowball, flattened etc) by enemies but that doesn't affect his nonexistent health bar in any way. While you may think "This actually makes the game piss easy, doesn't it?", this is far from the actual truth.
There are many things that will challenge you on this journey. Sometimes, you will have to reach certain locations or fight bosses without being hit, and this is surprisingly more challenging than it seems. Take for instance the first boss you will encounter, which is a Russian doll who throws hammers at you and tries to attack you through dual-wielding mallets once you destroy the barrels he is on. If you get hit by one, you turn into a spring and bounce out of the room where you fight him in. Whereas if you break down the barrels and charge him while he is stunned after, he will be defeated and you will be able to reach the exit and the treasure chest.
Or another example, you must fly to a key in order to open a treasure chest on an owl, but the room is a huge maze of spikes which you must traverse in order to reach the chest.
Or you might have to be affected by a certain condition to reach another area. e.g. getting stung by a bee will give Wario an allergic reaction, swelling his face and allowing him to float upwards until he hits a ceiling or an obstacle, then he deflates.
The game can and does challenge you and in the most inventive ways possible for a handheld game of its generation. This is why the gameplay is top notch.
Furthermore, the game is huge on backtracking. Occasionally, you can obtain items which enhance your current moveset either through new abilities or upgrading existing ones. These abilities can let you reach previously inaccessible areas. Not only that, but the vast majority of treasures that don't enhance your moveset will still unlock new areas. E.g. finding a cog which turns on a conveyor belt which makes a new area in a specific level accessible.
Audio - 5/5
The music is bright, lighthearted and colourful, and furthermore, its actually varied a decent amount. While you'll hear the same background music in a few levels. The game helps to keep it varied and each song actually matches the level it was made for.
There isn't much to say about the audio, apart from the fact that it was good, and I have no criticisms about it at all.
Lifespan - 4.5/5
Due to the large amount of conditions Wario can be affected by, and the huge variety of ways that boss fights and obstaclest can challenge you, Nintendo certainly have made one hell of a big game with a plethora of bosses and treasure chests.
In total, there are 100 Treasure Chests to obtain in order to fully finish the game 100%. Furthermore, you only have to open about 30% of these chests in order to actually reach the final boss. Of course, thats not a full clear, is it?
The point is that, this game has a medium lifespan. While it doesn't take too long to get everything (around 20 - 40 hours of playtime at the very most), this game will entertain you almost the entirety of the way. It could have been longer but for a GBC game, Nintendo did an amazing job.
Overall - 5/5
Wario Land 3 is a brilliant platformer with only minor flaws like some of the graphics (Which are to be expected on an 8-bit handheld console and was in no way due to bad development teams) and a few minor issues with the game's lifespan (Its huge but not collossally huge)
Nonetheless, the flaws are not significant enough to penalise the game in any way.