Super Mario Bros. is surviving on nostalgia alone. Look, it's a wonderful little game, it's simple, it kicked ass in its day, and it innovated. It's sold over 40 million copies, it's responsible for an unholy spawn of sequels, etc., etc. It's a great game, one of the best of all time. Awesome.
Deus Ex is better. Look, SMB can keep you happy for like, 2 hours, at best. Deus Ex can probably do more than 10 times that, and that's on one playthrough. It defies genre, it throws all kinds of gameplay at you, it has large environments, it's got a great storyline, and it's hugely replayable. It's action, it's RPG, it's tactical shooter - and fuck it, it's cyberpunk, which gets it points for the second best usage of "punk" (steampunk forever). Probably the biggest flaw you can point out is its dialogue and musical score, which can be lacking at times. Aside from that? Fantastic in every definition of the word. It's the recipient of over 40 Game of the Year awards, and is considered by most at least in the top 30 games of all time, and by many of those in the top 10. Now, it's true that that can be said of Super Mario Bros., but Deus Ex has a little advantage over it there - it's a better game in every class, and the only reason to vote SMB is if you're some deluded nostalgic.