Thats a hard one as I was on the blue team backing the speeding hedgehog so never really got into Mario until a few year ago.
I do enjoy it and Nintendo certainly shown how to do a 3D game properly with fluent controls. It is an important game and pretty much ground breaking for the time. Only gripe though is replaying each level to do different things, can be a little tedious at times, then having to collect absolutely everything which again can become a bit tedious and long winded.
With regards to most important games of all time I would put it in the top 20 I would say