Words can't describe how much I love this film. One of my childhood favourites from the '80s, and over 25 years later, it still holds up as superior entertainment.
First and foremost, it's a great story (okay, a little improbable but who cares!) with fun performances from Broderick/Hunt, and a (weall-earned) emotional, feelgood ending.
The 'acting' by the chimpanzees is a riot! Virgil - what a great character :-) Nowadays, they'd probably use CGI (Rise of the Planet of the Apes, anyone?), which would rob the film of its heart.
Another superb '80s movie I'll introduce to my young nieces/nephew at some point. They've already experienced the joys of Short Circuit, Flight of the Navigator, and Explorers, and this will be a worthy addition to their ongoing film education :-)
Special mention for James Horner's score; as a solo listening experience it's not one of his best, but in the context of the film, it works really well.