The e-Reader levels really highlight how much of a shame it is that Nintendo didn't make an original 2D Mario game on the GBA, basically the last chance we really had for a new sprite based Mario platformer. They're great levels with lots of unique and original ideas, and collectively are about as long as SMB3 itself is... just without the proper pacing of a fully structured game and also accessible only via an expensive peripheral and impossible to obtain cards. At least the Switch Online version has all the levels unlocked, though it comes with the unfortunate loss of the vegetable and fireball switches to add some extra variety to main game SMB3.