It's a traditional American fairy-tale. Protagonist has it bad, gets worse while working to make things better, and everything keeps falling down around him. Finally, through perseverance, life cuts him a break. What's so wrong with that? Well, apart from the rather dubious attitude towards his wife and her relationship with their son.
Mostly, the film never shows him being happy. It tells of his road to being rich. Unfortunately
rich==happy, though a common delusion in the West in general and the USA especially, evaluates
false. It's bollocks of the highest order, spouted by the very rich to cover up for their lack of any other fulfilment in their lives. The film isn't about the pursuit of happyness, no matter the spelling. It's about the pursuit of money.
The worst part is that if they'd made just one little change at the end of the film, I'd have been a lot happier with it. Racing to get on a bus, the kid loses Captain America, who has been a constant companion throughout all the shit that the pair go through. If the end had shown the protagonist using even the five dollars he got back to do something for his son by getting him a replacement Captain America, then I wouldn't think of the protagonist as a soulless hypercapitalist tosser with no regard for his family beyond indicators of his own worth. I'd have thought of him as an occasionally flawed but generally decent human being. But no, he's rich thus he is happy. To hell with symbolic gestures or demonstrations of love towards the child who is now only a trophy of his victory over his wife.
If they'd done that, I'd have been very happy. As it is, while I think it's a great film, the main character turns me right off the story. In the end he's to much of a cunt for me to find him sympathetic.