Not a fair comparison. Yes, I have over 400 lives because of all the coins, but Mario games have been giving out lives like crazy since Super Mario Brothers 3. Lives are a terrible comparison for challenge. I also had 200 lives in Super Mario 3Dland, and that becomes one of the hardest games in the series.
The game is not nearly as challenging as SM3DLand' s second half or even New Super Mario Brothers, but it is somewhat more challenging than New Super Mario Brothers (aside from not having to fight any bosses with a mini mushroom). Second easiest Mario platformer is probably not an unfair assessment.
As for levels which require perfection, that's mostly the cannon levels, at least as long as you don't go in as raccoon mario (which for those levels is almost as good as using a P-Wing in Mario 3). Go in as small mario and they are brilliant examples of the precision available in a Mario game, and show how a Super Meat Boy style challenge could work if Nintendo chose to do so (not that they are that hard, but they give the idea).
The only problem is that there aren't nearly enough cannon levels. There are only
There are a handful of other levels with some precise platforming needs, but it really leans more towards clever secrets and inventive use of established mechanics than for challenge. The handful of levels that are tough are usually short enough that you can get past them fairly easily.