I agree with the majority of responses here. Wait, preferably longer than a week or two. Wait until the story leaves your mind, when you can go a day without thinking about it. Give yourself that bit of distance, and when you finally pick it up again you'll be much more objective, that's true, but also excited by what you've written. That excitement will help you get through the rough spots, the parts that need drastic change or simply don't work. You won't feel quite as dejected because you're rediscovering all the good parts that do work, the parts that thrill you, the parts you can't believe were written by you.
That's my experience, and I've read similar experiences from others here. I have stories that I edited and rewrote soon after finishing and thought they were done, but when I picked them up a few months later I've always been able to polish them further. For the ones that I let sit before reviewing, after a few months I find I'm still content with them and usually find myself wasting time with minor tweaks that aren't even necessary.