I recently watched Spirit and enjoyed it very much, I've seen it about 4 times now on HBO and will buy the DVD. Those who gave negative reviews would probably think that `Vanishing Point' was just another car chase movie and `Thelma & Louise' was just another chick flick. Although the conclusions of those films are darker I feel the themes are somewhat related; that freedom and individualism are very important and that there is usually someone wanting to take it away from you. The other common trait of these movies is the caring, thoughtful `guardian angel' types who help the main characters to overcome adversity.
Another review here mentions how this film relates to the theme of civilization invading someone else's home. All one has to do is look around at the dwindling open areas around us to see that.
I thought the animation and the story were amazing, the animators really got the horses to look, act and move naturally. Spirit's emotions were very clear as the story progressed (yes I'm aware they do humanize the horses a bit, but this is fiction). In a couple of action scenes you feel caught in the current of the rapids and the heat from a forest fire. In other more quiet scenes (which are most of the time) you're allowed to savor the backgrounds. One of the big things that make the story really work is by not going the talking, singing animals route. Doing so would take away from the story's power. Instead the flow of the story is told by occasional narration by the main character, further punch is added by the fantastic soundtrack. Another plus is that they weren't afraid to give the story somewhat of a dark side (which really made this film watchable to me). This isn't prevalent through the entire movie though, and the conclusion is fitting and uplifting without being sappy.
Those who appreciate horses will really like this movie, but I think it's a bit more than a horse movie. I don't feel this would be a good movie to take children to if they're brought up on the inane fare that's offered up today. But if they're the thoughtful sort that can handle compelling stories like The Lord of the Rings and Black Beauty they'll likely love this movie. Hell, I'm 35 years old and STILL love that stuff.