Quartet is another one of those movies (see also The Best Exotic Marigold Hotel) that boils down to "Aren't old people adorable when they keep on having relationships, and feeling emotions, and doing things, just like regular people?"
There's nothing remotely surprising about the story, so the movie is entirely dependent on the charms and talents of its cast. But when your cast consists of Pauline Collins, Billy Connolly, Tom Courtenay, and Maggie Smith (with Michael Gambon in the biggest supporting role), those charms and talents are not inconsiderable. For me, they were just enough to carry the lightweight material.
The setting is Beecham House, a home for retired musicians. To be precise, a home for retired classical musicians; this is a place where most of the residents are still not convinced that The Beatles were a good idea.
The residents are preparing for their annual fund-raising gala, at which they sing and play in hopes of raising enough money to keep the place open for another year. The arrival of the newest resident (Smith) gives the gala's director (Gambon) a brilliant idea -- the four principals should perform the quartet from Rigoletto, an opera in which they once famously co-starred. But Smith is reluctant to perform at all, not wanting to "betray who I once was," and she's particularly reluctant to perform with Courtenay, because They Have A Past.
It's nice to see Smith in a role that's a bit softer edged than her current default setting (though she does get off a bitchy zinger or two), and she and Courtenay are delightful together. Connelly is in perpetually horny and uncensored mode, which he can do in his sleep, but he does it with great panache. Collins is very good as the woman who's always been the ditziest and most absent-minded of the group, characteristics that are starting to shade into senility.
Nothing essential, but it's pleasant light entertainment, and it'll keep you charmed for an evening when the DVD arrives.