I found Montage of Heck to be a scatter-brained documentary that couldn't decide which direction to go. It grabs at various forms of media culled from Cobain's family, and tosses them into a blender, with splashes of interviews and band footage.
There were some stunningly rotoscoped animation, using narration from Cobain, that briefly takes you through his dejected teenage years in Aberdeen, Washington. They also rendered the years Cobain spent living with his first girlfriend, Tracy Marander, who supported him when Nirvana started getting noticed. Marander isn't shown (only in interviews and rare photos), we just see how Kurt spent his days being creative while she was at work. Anyway, not long after, the band signed to Sub Pop and released Bleach.
There were also drawings and writings (many would make Jack Kerouac's "spontaneous prose" seem lucid by comparison) from his sketchbooks / journals, that were brought to life using muted computer graphics. These were scattered throughout, and became laborious after about the 10th time. Still, the music that accompanied them were great. We get to hear plenty of unreleased material, and I even noticed some Nirvana covers, which felt redundant.
Now, cue in Courtney Love. Sigh. It was annoying seeing her all dolled up by a makeup artist, chain-smoking and sounding incredibly untruthful about Kurt's last couple of months. I won't ruin it, but it's towards the end of the film and it made me more suspicious of her. The home videos of Kurt, Courtney, and Frances Bean were quite touching, although at times it got dark, especially some moments with just Kurt and Courtney (not 100% on who recorded them). You know he was the happiest he's ever been, but they were also plunging into the abyss of heroin and other drugs.
Overall, Montage of Heck started off as a sweet concoction that ultimately left me with a bitter aftertaste. I hear that 'About a Son' is the superior documentary, so I'll watch that in hopes of getting a deeper insight into Kurt Cobain and Nirvana.