Great cast, Breslin especially.
I've been a Bruce Willis fan since the '80s, but he doesn't make this movie magical on his own: Spencer Breslin is fantastic as little Rusty, Emily Mortimer is effective as Amy, the optimistic foil to Willis' cynical Russ (and it looks like she and Breslin have a genuine affection for one another), and Lily Tomlin delivers the best sarcastic replies as Russ' assistant. There is also a charming brief but pivotal second scene with Jean Smart.
One thing to note: due to Russ' shame over his childhood self, he levels criticism at little Rusty (words like loser and chubby) that would otherwise be cruel were we not supposed to know that he's talking to himself. Every time I watch this movie (and I watch it often - it's on cable constantly!), I wonder how much had to be done to prepare Breslin for the name-calling scenes.