I took my wife through her first SAB last night, with the warning that World 2 was a significant jump up in difficulty compared to World 1. It had been a few years since I did World 2 myself, but I did recall the difficulty spike that I warned her about.
What I had forgotten, though, was the overall tedium of Zone 2 and 3. Zone 1 is fine - it's a bit longer than World 1's zones, but not too much so, and has a nice little break up mid way with the raft before moving onto the final two little segments. It feels like a good, natural progression from World 1's zones.
Then we got to Zone 2 and 3, and I was quickly reminded why I hated doing these the first time, and never did them after. They're long, tedius, and just not fun to play through. Worst yet, the exploration of the zones is lackluster compared to the ones in World 1, given that the zone are much more linear than the original World's 3 Zones. The Smile paths do help a *little* in this regard (like being able to completely skip the stupid trap pagodas in Zone 2), but it doesn't help the other problems they have - mostly how awful the combat is in SAB and how it's the focus of Zone 2, and how both Zones vastly over stay their welcome., which is a shame because aesthetically they're really cool, and the bosses in Zone 3 are a lot of fun, but honestly by the time you get to the Yeti and Storm Wizard/Dragon, you're just kind of at the point of exhaustion where you're just throwing yourself at the boss until it dies.
The only real saving grace is that there's no reason to do World 2 a second time after you've completed it on your first play through, but that's not really a saving grace so much as just a desire to not want to return to them out of the tedium. It's not even a case of World 2 being too difficult - my wife used ten continue coins to get fifty lives, and went through maybe ten or fifteen of them to get through the entirety of World 2. Her biggest complaint, and mine as well, is just that Zone 2 and 3 are too long, plain and simple.