Wonderful. Mario games still achieve a level of fun no other games can match.
I'm not sure Super Mario 3D Land was the best game released last year (whatever that means), but it was the game I most enjoyed playing. From the moment I turned it on, I was having a blast. The simple act of controlling Mario remains a joy after all these years. Forget objectives, boss fights, collectibles, and secrets -- each of which also contributes to the enjoyment -- it's fun just to physically manipulate Mario, run him aimlessly around levels, bopping enemies, and bouncing off walls. No other game comes close to duplicating this experience of moment-to-moment joy and whimsy.
Of course the overall game structure doesn't disappoint either. There are tons of levels, tons to collect and unlock, and no shortage of variety in levels or abilities -- this is a Mario game; you know it's going to be a full, diverse experience. (We'll ignore Super Mario Sunshine for a moment.)
A special note should also be made for the use of 3D in this game. I was a huge skeptic of 3D in all applications after experiencing it in movies and then on the 3DS. But this game (as well as Mario Kart 7 after it) restores my faith in the technology. The 3D doesn't fundamentally change the experience but it definitely adds to it.
The only complaint I could level against the game is that it's a little too easy. Even some of the late-game stages are easily breezed through. Still, you'll hardly notice the below-average challenge when you're having this much fun.