I had the 5S now for a few days now (upgrade from the 4S) and I really like the speed. After I got the phone, I tested the difference in speed by opening up some games that I know need some significant processing power, like Infinity Blade II, and just starting the game took time with 4S while the 5S just opened up with no delay at all. The fingerprint scan does recognize your fingerprint well regardless of how you place it on the sensor, which is pretty cool and you can register as many as you like. There are some times it doesn't read and if it can't recognize your fingerprint after 3 tries, then you have to input your unlock code (difficult password if you chose that setting). Doesn't happen often, but it's really just a minor inconvenience if that does happen.
I did test out the slo-mo camera by filming my kids playing and there is no drop in quality compared to taking a regular video. What I like is when you do playback, you can customize what parts of the video you want to slow down to 120 FPS. I did try to upload the video onto youTube, but it always says that the upload was unsuccessful. I haven't researched enough to find out why, but I just don't think video is compatible to upload.
For iOS 7 in general, overall I like the upgrade and really didn't find too many things I found to be an annoyance. The control panel you get from sliding from the bottom-up is a significant improvement compared to the last they had and I like how it's accessible without unlocking the phone.