From the Toronto Film Festival, this is the review at Roger Ebert's website:
But it (the movie) all depends on the deadpan chemistry between rascally Vin and wee Oliver (with an assist from Vin's adorable Persian cat, whose face is like a smooshed-in pumpkin). I am happy to report that Murray has found one of his best playmates since he and Ms. Scarlett made the rounds in Tokyo during "Lost in Translation" in young Mr. Lieberher, as they share questionable after-school pursuits. That the audience broke out in applause over Vin's aggressive mode of intervention after Oliver is set upon by a trio of bullies proves that his mom wasn't so wrong in her babysitter choice.
This is one of the best kinds of Murray showcases, one that allows the 63-year-old actor room to do his funny stuff, do a little dance and sing a closing credits song and–even more impressively–get a chance to reveal by the final third of "St. Vincent" that he is also a fine dramatic performer, too. All I know is that I am itching to try out his response to a telemarketer–"Come on, coward! Try to sell me something!"–just to see what happens.