Without giving anything away, here's a reference to another one of Spielberg's works to try to explain what the ending of A.I. is like:

Imagine that we're at the very end of Saving Private Ryan.  The old man is standing by the grave, asking his wife if he's led a good life.  We fade out to the American flag...and then fade back in.  German tanks roll over the hillside, laying down mortar fire at the old man and his family!  Tombstones are blown apart!  Everyone runs for cover!  Then, some dinosaurs come running onto the scene and start eating people!  



That's what the ending of A.I. is like.  Haley Joel Osment is SUPERB--he deserves a medal, a monument, and a cookie for his acting; Jude Law is damn good too.  But, the last 30 minutes of the movie are completely trivial and actually serve to detract from the story.  Everyone's reaction in the theater I saw it in was pretty much, "What the hell is THIS?!"  You can definitely see where Stanley Kubrick wanted to end the movie, and everything after that point is pure Steven Spielberg gotta-leave-the-audience-with-a-feel-good-ending tripe.

Oh, and I could have lived without the cute teddy bear pervading every scene in the movie. And one more thing: HOW THE HELL DID HER HAIR SURVIVE INSIDE A TEDDY BEAR'S POCKET FOR 2000 YEARS WITHOUT DISINTEGRATING?