You're all missing the point.
Imaginaerum is far from being your standard "introduction, conclusion, development" story type.
It's a vignette, a snapshot of the tumultuous mind of a creative genius struck by dementia.
Intentionally or not, the level of symbolism in this movie is fantastic, but you have to look for every details' meaning before really enjoying it.
A a safe bet would be to say that all the surrealist scenes are representations of Tom's memories, psyche and confusion. A not so safe bet: the dream is not actually Tom's, but his daughter's.
Here are some of the aspects I like the most:
The suicide scene:
Tom looks at himself looking at his father, but his 'traveler' self, as opposed to his 'memory' self, dares looking at his father face to face. Tom finally faces the reality of his father's act buy looking at the scene as a third party.
Then, adult Tom throws the dancer away, in sync with the death of his father, the link between the two events, one triggering the other, is represented in the most beautiful manner.
The rails
"It's lifeless"... the rails are ways through Tom's mind, inside his own head. Now dementia has taken over, the rails are broken. Once again, a beautiful symbol.
The 'song of me'
All along the movie, sheets of that song are scattered around. Tom's most precious memories, being defiled by the snowman, dug-out by the daughter and finally revealed by old Tom.
The snowman
I don't really like the choice of a snowman, neither do I like its design. Its symbolism though, is really strong. The snowman is both Tom's father (as a trigger to his downward spiral into madness) and depression/dementia.
The french soldiers
Someone said Dali? Magritte?
In the end, if there are some flows (the acting could be way better, but then I've seen worse, some green screen scenes are too cheap looking), this movie, which is not completely a musical movie, not a traditional story and not really fantasy, rests on a solid base of memory/interpretation theory and is a gorgeous moving portrait.