I never really found SMB3 to be all that difficult. Even though I've professed before my favoritism towards SMW as the better all-around game, it was still pretty difficult to get 100% completion in it. Actually getting to Bowser's castle was no easy feat either, but I actually got there by stroke of luck (and some help from Star Road exit 4) and got to "completing" the game within about 2 years. By contrast, I went around zig-zagging and beating the baddies in each SMB3 level within a week's time, and I just didn't get as amped up by the various power suits like every one else. Both games were a testament to how good Nintendo's games were back in the mid-80s to late-90s, but each game might have gone after a different niche of player, I thought.
But... to aid in your argument, I recently found this article by accident that details a list of the top games that shouldbe ported and redone in order to be playable on the new (I'm not sure how new this system is) Nintendo 3DS.
The Top 50 Games That Belong On the 3DS - UGO.com
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Visual Architectonics]