J. Edgar is exactly what you'd expect a Clint Eastwood biopic to be -- overly reverent and a bit stodgy. It's salvaged, to some extent, by some fine acting.
The story jumps back and forth from the late 60s, when Hoover is dictating his memoirs to an assortment of young agents (all of them strikingly handsome), to the 20s and 30s, as we watch Hoover's version of the events in question. (The movie mostly skips over the 40s/50s.)
Leonardo DiCaprio is quite good as Hoover, though his accent does wobble a bit; he does a fine job of capturing the mix of patriotism, paranoia, and narcissism that made Hoover so dangerous when given power. Even better is Armie Hammer as his longtime companion and assistant, Clyde Tolson; Hammer is particularly strong in the movie's last act, doing a superb job of capturing the physical and vocal debilitation that followed Tolson's stroke.
Eastwood fills the movie with a lot of marvelous character actors who make strong impressions in small roles -- Stephen Root, Zach Grenier, Ken Howard, Josh Lucas, Jeffrey Donovan (as Robert Kennedy).
The movie is less coy than I'd have expected about the precise nature of the relationship between Hoover and Tolson, though Eastwood and screenwriter Dustin Lance Black aren't willing to make a definitive statement that they were lovers when we have only circumstantial evidence.
The old-age makeup on DiCaprio (and on Naomi Watts, as Hoover's longtime secretary) is quite good; Hammer's is significantly less so. Eastwood has yet again scored his own film, which is yet again a mistake; his standard piano noodlings give everything the feeling of sepia-toned elegy, which is only occasionally appropriate here.
On their own, the screenplay and direction wouldn't be enough to recommend the movie, but the performances are strong enough to make it worth renting when the DVD arrives.