I really struggled to get into Wario Land 3 because of how his abilities are progressively unlocked throughout the game. I think going straight into this game after beating Wario Land 2 was quite jarring since you begin with barely any abilities at all, which just put me off playing for ages.
However, once I did start unlocking more abilities, I found the game a lot more enjoyable and started to appreciate the level design and how they introduced new ways to approach each level once you unlock new abilities and power-ups. Although I feel like this concept just isn't really for me, I love the feeling of realising a power-up I got will allow me to reach something I noticed on a previous level, but I think I prefer when that's used for secrets as opposed to required level progression. Also playing the same level 4 times just feels a bit repetitive sometimes, even though the level is slightly different each time.
The boss fights were pretty hit or miss, I especially disliked the ones where it only took 1 hit for you to get thrown out of the fight, then have to climb all the way back up just to try again, those were very annoying, but there were definitely some stand-out ones that I really liked, like the football match against the rabbit which was very reminiscent of the basketball boss in Wario Land 2.
Overall, I appreciate and respect what Wario Land 3 is and how the series is constantly trying new things resulting in there never being a stale moment, but it just wasn't really for me.