The first time I fired up Braid on my laptop, I was immediately struck by the lovely and lush environments — 'It's like stepping into a children's book!' — that gelled together in a visually pleasing way. Puffy clouds and suns hovered over pale mountains, forests made up of brilliant yellows — whatever it's other merits or lack thereof, I loved the visual look of the game. David Hellman, who created the art for Braid, goes through the process of creating the visual look of Braid, from "programmer art glory" to finished product:

Braid had already appeared at two GDCs before I ever got involved. Jonathan Blow, its creator, showed Braid's time manipulation puzzle-platformer gameplay at a couple Experimental Gameplay Workshops, and an Independent Games Festival, where it won an award for game design. Minus some polish, it was nearly a finished game: playable, coherent and individualistic. Visually, though, it was primitive. Its blocks, spikes and ladders were utilitarian, communicating merely the elements of platformer-ness. It could have remained a visually simple game, but it already contained hints that it wanted to be more, to express itself across the full multi-media palette available to video games. ... Hired as visual artist in the summer of 2006, my challenge was not only to clearly present Braid's mechanics and behaviors, but to help tell a story that was anything but literal: part anecdote, part artifice, part philosophy.

It's an interesting article even if you're not terribly interested in Braid, as it goes through the art creation step by step with lots of screens. It's an edifying little essay. The Art Of Braid: Creating A Visual Identity For An Unusual Game [Gamasutra]