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I started the Metroid series with Prime, and going back and playing Super Metroid after that was like "hey, this feels like a Metroid Prime demake!"

(I know that's not really what you asked, but that's what the thread made me think of)

Yeah, another good one. Done in the style of Sam and Max Hit the Road that could be amazing.

I would like every Monkey Island game from 3 onwards to be remade in the pixel style of the first two games.

Deus Ex: The Fall done like Deus Ex: Human Defiance. It's awesomely hilarious to see people more enthusiastic about an April Fools joke than an actual game release.

Warcraft 3 with 2D sprite graphics. Like Starcraft, but maybe with higher resolution 2D graphics (I think SC was only 640x480).

Maybe not a biggie, but I somehow disliked the move of Blizzard RTS games to 3D. The game screens in WC3 seem cramped and it is hard to tell whether some area should be accessible or not.

On the other hand, I feel Age of Mythology moved the "Age of..." RTS games pretty nicely to 3D. It almost doesn't feel like 3D, but better looking 2D graphics. The only thing I didn't like about that was that towers and such wouldn't be placed in exact lines like in Age of Empires 1-2. If you wanted straight lines, then you had to try to place each tower pixel-perfectly.

Bioshock Infinite. Get rid of Booker and turn it into a point & click adventure.

Diablo 2 as a tower defense game, like Defender's Quest .

Any of the casual games where people have large heads and big eyes and look like children in an old 2D style where the heads are just a few pixels.

Borderlands topdown like Ikari Warriors.

I agree with this.

Age of Wonders 2: The Wizard's Throne and Age of Wonders: Shadow Magic with less cheerful and darker graphic of the original Age of Wonders. That would be amazing!

They actually did this with Dark Void, making Dark Void Zero:
http://store.steampowered.com/app/45730/

Not that Dark Void would be at the top of many people's de-make lists but, just saying!

(was also done 3 or 4 time with serious Sam, of course! Oh and Mega Man went backwards too - MM8 and 9 returned to retro 2D)

The Witcher?

Also, both Baldur's gate: Dark Alliance games. Back to the Infinity Engine with you, where you belong!