My main character is level 53 and many, many hours of playtime, and sure I've spent a lot of time in Riften, but for some reason it wasn't until recently that this city began to grow on me, and now I consider it my favorite city in Skyrim. It's definitely one of the most beautiful, especially at night. The weather is a little crappy but if you use Clear Skies that's not an issue.
And thanks to patch 1.9 I was finally able to become the Thane of Riften (well, I also never really pursued it that hard), and man the view out the backdoor of Honeyside onto the water is the best of any player house in the game.
Plus Riften's got some of the best NPCs in Skyrim. Mjoll and Marcurio are very unique followers, and I always love having them along with me.
Anyways, I felt like I had to do some praising of Riften, and thought this might be a good place for anyone else who wants to wax poetical on what they love about this city.