Looking back at New Super Mario Bros., this game is actually more different to the other games in the series than I would've thought.

This becomes immediately obvious in the level design: Layouts are often structured with less space for the player character and are less focused on player movement.
This leads to a bunch of cool ideas that appear in no other New Super Mario Bros. game, but it also means that levels often felt less satisfying to jump around in.

The secrets were sometimes too obscure to my liking without any real hints pointing you towards them or required powerups that you couldn't get in the level itself.

The new powerups were something of a mixed bag.
I personally loved the blue shell and mowing over a row of enemies and being able to destroy brick blocks.
The mega mushroom on the other hand felt more like a gimmick without much use for it; in fact I didn't use it most of the time out of fear of accidentally destroying the path to a star coin.

My only complaint about the music is that there was too little of it, the few tracks that are in the game are fitting, but get reused too many times.

Don't get me wrong, this is still a really good game: The controls work perfectly, there are unique and interesting boss fights and the multiplayer and minigames are great additions to the main game!
All in all, I definitely enjoyed my time with New Super Mario Bros.