I've used SFML for a while now (used GLFW or SDL before, couldn't get SFML to compile.. then I finally updated my compiler) and I feel like, while it's a great library as a whole, there are a few things that I dislike about it. Decided just to put them in one post.
1. Modern OpenGL. I know this was something that has been suggested before (and likely several times), but this is very important IMO. EDIT: Looking through the rest of the forums, it looks like this request is a lot more common than I thought. Based off of that, I'm guessing this probably wont happen at all, or at least not before OpenGL 112.8 comes out...
2. Put the graphics into it's own class, no drawing directly to sf::RenderWindow. That's just a very weird way to draw things.
3. What's up with the whole sf::Sound|sf::Music thing? I know the difference, but the names suggest how it's used, instead of actual underlying differences. Why not sf::BufferedAudio|sf::UnbufferedAudio, or even sf::Audio|sf::AudioStream, just something meaningful. If possible, something like sf::Audio audio(sf::Audio::Stream); would also work.
4. Texture loading (or any asset loading, for that matter) should be in a separate module. Most applications need some library to load their assets (PNGs, WAVs, etc), but not all of them want a fancy, possibly even bloated, wrapper.
5. This is more of an insignificant opinion than anything else, but I'd like to see the window resizeable option during window creation a part of the video mode, not the style. Like this: sf::Window window(sf::VideoMode(800, 600, true), "", sf::Style::Default);. It just seems more natural to put the option for a resizable window alongside the initial window size rather than in the window style.
Can't remember any other things I didn't like. Guess that's a good thing, though.