Unity 5 may be a bit tough at the beginning, specially when dealing with the new lighting system (GI, Global Illumination). The Continuous Baking feature (enabled by default), the insanely long baking times, the lighting settings having unclear effects, and the dense and hard to read documentation can make the experience a bit frustrating at first.
You can have decent baking times while prototyping in the Editor, turning the new GI into an actually enjoyable experience. Quick hint: set Realtime Resolution to 0.01 – 1, and Baked Resolution to 1 – 4.
I’ve written a little reference guide describing the essential GI concepts you must have in consideration, and how to deal with them and their settings in the scene. It should help you to get used to GI within minutes.