I absolutely love the first 20 minutes when they're back in 1955. I wish they went with dual perspective and kept one Doc in the Old West and the other two back in the quiet solitude they cultivated for this return to 1955. Doc's house in the rain, the library, the drive-in theater...terrific atmosphere.
All three "Back to the Future" were something more than time travels, temporal coincidences and physical paradoxes. It's the bittersweet feeling that emerges on screen with the romance and adventure that comes along by these two different characters that blend perfectly in this Great Scott-experimentation. The truth is that the 80's were great times to make entertaining and brainy sci-fi movies for the whole family.
A combination of science fiction and western is great and works perfectly. I love the ending which is really satisfying and is definitive making any revisit practically impossible. This entry is slower paced and feels more relaxed with less effects. Western haters will probably be more annoyed that this final outing ends up here, but I feel it is perfectly in tune with the rest of the series.