When I first started Princess Mononoke, I really wasn't planning on enjoying it. Studio Ghibli films have a tendency to bore me to tears, and environmental films fill me with rage and an irrepressible urge to chop down forests and strangle vegetables (I guess I'm just contrary). So the prospect of an environmental film from Studio Ghibli makes me cringe (I had a terrible experience with Nausicaä). But my roommate was watching it, so I broke down and accompanied her. And was pleasantly surprised. It was gorgeous, and hardly made me angry at all! (Probably due to the "human" side and "nature" side being roughly equally flawed, whereas most in the genre portray nature as PERFECT FOREVER! YAY!, and humans as EVIL FOREVER! BOO!)
If you're a fan of Miyazaki, you'll adore this. If (like me) you aren't, well, you'll probably enjoy it anyway, despite your better judgement and the terrifying character design of the forest spirit.