I was thinking: Was Wario Land 4 made so great on purpose to show off what the Gameboy Advance was capable of? I mean, its graphics, music, sound effects etc. are among the best of GBA games. And since the two previous WL games were on the Gameboy Color, this seems quite likely.
Well, it's clear the people working on it enjoyed making the game and put their heart and soul into it. So in that sense, it was definitely made to be a good game on their part. They likely had about as much passion for this as the team behind Yoshi's Island had for that one (which even came with a secret message saying the same).
But was it made to be great? Well, maybe. Nintendo didn't generally half ass most of their major games back then (or even now to be honest), so it was clear the intention was for Wario Land 4 to be at least be a good fun game to play. And yeah, it was definitely made to show off some of what the GBA was capable of. After all, the original games were meant to show off what the Game Boy and Game Boy Colour could do. They were literally some of the most advanced games on the system.
However, I'm not sure the developers sat down and specifically said 'this is going to be the best GBA game ever' and 'someone is going to write a book about this in 10 years or so'.
