Kdenlive is great if you just want to edit some holiday movie or pictures. In my experience, the resulting movies look good, and any ugly problems can be associated with the limitations on my camera, not Kdenlive. It's an easy user interface, and it only gets complicated when you want to do more advanced effects (the complexity comes from the number of options, meaning you have to go through some menus and try out a bunch of things). Btw, last time I used Kdenlive, I used Linunx Mint 16, and had no problems with audio (or any problem in general). Also, the crashes that I used to experience in 2012 seem to be gone completely.
I also used SlowMoVideo, to make slow motion videos and to speed up videos (which I then put into Kdenlive to become part of a larger project). It works, although its user interface has a rather steep learning curve (not the most intuitive interface). It lacks a simple method to just slow down or speed up a movie by a factor two. It appears that the makers expect people to want to use the full range of options all the time. (I realize that asking for less options will upset some people... sorry).
Finally, I also used Pencil to make some animations. In my case, quality was poor, but that says a lot about my drawing skills, and little about the program. What I missed a lot was an easy method to stitch a series of pictures together into a movie. I think that Pencil claims to provide one, but I never got it to work. In desperation, I used some awful command-line tool and it took me ages to figure out the exact code to type in to get the desired effect.