Actually, Metro 2033's improved Redux version is less like a facelift, and more like a full-body transplant.
The original title in 4A Games' post-apocalyptic shooter has been completely redone in the developer's 4A Engine, enhancing the game's graphics, performance, level size and mechanics. Check out a few clips of gameplay from Metro 2033 Redux above to get an idea of what's been nipped, and what's been tucked.