What I also like about this movie is that there are-refreshingly- no villains. The Champ's former wife and her husband are decent and kind, their young daughter eager to accept Dink as her brother. They also behave very well to Champ- better than he deserves, frankly. Champ isn't a good father, but he does love his son and, in the end, it is this love which motivates him to pull himself out of the drunken stupor he's been wasting his life in.
The only part of the film which I don't particularly like is the very end, which people generally either love or hate. I personally find it a bit overwrought and over-the-top, but that's just my opinion and in any case, the rest of the movie is good enough to forgive a somewhat flawed ending.