Whether you love or hate the idea of HD remakes of classic titles, it's fascinating reading up on just how much work -- and deliberation -- there is involved in scrapping a game's entire visual canvas and starting over.
When a company remakes a 3D game, it's not that dramatic! We usually see an increase in the number of polygons, maybe some new effects, a higher resolution, but there's no doubt what you're looking at is an improved version of something, not a total overhaul.
Older games employing pixel art, though, have no such luxury. Because they were originally drawn at such low resolutions, when they're re-released for modern hardware they often need to have everything -- from characters to backgrounds to menus -- remade.
This Gamasutra post by Lars Doucet gets into the nitty-gritty of the options available to studios remaking the classics, what works, what doesn't work and what should be applauded.
Weirdly, Square Enix can get it right (Final Fantasy I, below) as often as they get it wrong:
Some of the stuff in the post might be a little too technical for the general reader, but if you're someone interested in HD remakes -- or, real talk, you mess around with emulators -- it's a good read.