I have played quite a few action puzzle games over the years (though not those two specifically) and I definitely consider myself to be a fan of the genre.Do you normally like Action Puzzle games like Toki Tori on GBC or Chew Man Fu on TG16?
I'm a couple of worlds ahead of you and I've enjoyed the game so far. I can't say it's been super challenging, but I also won't say it's a bad game.
I think most people mean that it's a good game by Miyamoto that isn't talked about much when they say it's a "lost gem." You also need to look at the time period and console it was released one, I'd say Mole Mania's graphics and production is on par with many GB games at the time. It appears to be running on the Link's Awakening engine.
The game does get more challenging, but it's an action puzzle game so don't expect it to shift into some completely mindblowing territory.
Also, I have been playing through old GB games on my 3DS for the past year, so my experience is not owed to a lack of understanding of the GB's capabilities.
One additional thing I'll add to my last post is that I so far haven't once felt a sense of accomplishment while playing. So far I have just felt like I'm going through the motions.