I'm really excited to bring my 3-year-old on it. I think he'll love it. (And my 6-year-old, for that matter.) My husband and I rode it when we went on a weekend trip for just the two of us earlier this month. It's really fun. Like others said, it's a notch above Mine Train in intensity, but it's smooth.
But it depends on the kid.
The only ride so far that had made my 3yo hesitate is Haunted Mansion (he says it's scary or spooky, one of those) and all he talks about is being tall enough for Splash Mountain on his next trip (he's almost there... over 39" now... we'll see).
My 6yo (who *just* made it to 44" in December, when she was still 5) was allowed on everything at that height requirement except FOP and has loved it all, except Dinosaur. I regret bringing her on that one. I think Space Mountain made her a little nervous, but she still wanted to ride it again. Yet she loved Everest, which is obviously way more intense. It was the dinosaurs and darkness that got to her.