I'm sorry, I disagree. There's a saying, Love at first sight. It is a rare occurrence but it is certainly true. The problem is being just "pretty" just does not cut it; it has to be mind-boggling, jaw-dropping, drop-dead gorgeous in order to win hearts and minds. Most apps designers and developers can't recognize that and so they settle for "pretty" and when that product fails, that makes it seem like being beautiful is not very important.
I'm a graphic designer and there's a lot of talk going on nowadays that undervalues the real job of a designer, the part of the job that "makes things pretty". I think that is the first and foremost goal of a designer otherwise you shouldn't be even called a designer. I believe a designer should not just make things pretty (mediocre), but make it outstanding and gorgeous and keep focusing on that aspect to create a great product.
What's the point of a great user experience if people are turned off by the looks? And isn't a look and feel actually part of a memorable UX? You definitely need to be "Pretty First". That said, pretty alone is not enough. Combined that with a functional product and you get a winning formula.