This may be Spielberg laying on the sentimentality, but he is the master of it, and in anyone else's hands this film would probably be a disaster, but he is such a competent director that you can't help but be swept along by it. You really care about Joey, and the people that take him under their care.
The opening set-up is very long and could probably have used a bit of cutting, as they aren't that exciting, it's pretty much this : bloke buys a horse, it ploughs a field, and saves the farm. That takes about half an hour of screen time. The main point of this part of the movie though, is to build up the relationship between equine star Joey, and human star Albert (an excellent Jeremy Irvine).
When war breaks out, and Joey gets taken away by soldiers, we then follow his journey, with various new owners, through several different places, and everyone that comes across Joey seems to form a bond and attachment with him, and this includes us in the audience. There is a lot of action which follows, and even in the quieter moments (like when Joey ends up with a French farmer and his grand-daughter - a brilliant small role for Celine Buckens, who forms the best relationship with Joey, other than the central one with Albert), it remains exciting.
The moment that the film arrives at the Somme, it becomes very heartfelt, as always when a film features WW1, you know most of these guys are going to die, and rather pointlessly. One of the films best action shots sees Joey running, terrified, through the trenches and into no-mans land, getting caught in barbed wire, eventually resulting in an amusing truce between warring soldiers, as they try and set him free (a fantastic scene all round - acting, writing and directing).
The only real problem is the ending, although it was always going to happen, it is all just a little too convieniant, and designed purely to bring tears to the audience (in the screening I was in, people were openly bawling - I just felt it was a little overwraught), and reminiscent of the totally unbeievable end to War Of The Worlds, but it would have been difficult to end it any other way really.
Still a top movie though, and another success for Mr Spielberg.