The Lost Levels is an exhibition of game designer's sadism. Thanks to saves after each level on SNES they lead you through all these tough levels as in museum and say like: look, that's how we made Famicom players suffer back in the days.
Honestly levels themselves look pretty fun when you have infinite amount of attempts but you won't relax playing them. That's a bad thing about the game. Despite you put a lot of efforts beating the game you don't satisfy. I assume that's because complexity level is abnormal here and it feels artificial. So as for me I just wanted to complete the game sooner and not return to it anymore. Just to try on my own all this complexity and to put it into backlog of completed Mario parts.
I several times imagined myself beating it on Famicom without save possibility. I believe I would spend months or maybe years to do it :)
In general it looks more like DLC for original Super Mario Bros. But all the history behind the game makes it must play for Mario fans. But perhaps only for them.

"For Super Players" is a more apt subtitle for this game, as its design seems very intentionally off-putting to folks that weren't already intimately familiar with first Super Mario Bros. and willing to put up this sequel's sometimes-questionable sources of added challenge.

However, I grew up playing it a lot with the SMB Deluxe port of worlds 1-8 and the All-Stars version, both of which had a more forgiving continue system and allowed me to master the levels. These days this game is legitimately more fun for me to revisit than the original SMB1, as the SMB1/2j physics feel pretty satisfying when you have command of them, and these levels still give me a fair bit of challenge compared to SMB1's.

I can definitely understand why this wouldn't be most folks' cup of tea, and US's SMB2 / Super Mario USA definitely left a far more far-reaching cultural and series impact, but I appreciate it a lot for what it is.