The Untouchables (1987)

Never stop fighting till the fight is done, here endeth the lesson.
As good a gangster movie that has ever been made as DePalma does justice to Mamet's electric script. The acting on show is right out of the top draw, the inevitable ease that DeNiro puts menace into Capone is quite impressive, whilst the fresh faced pugnacious tenacity of Andy Garcia's George Stone is something of a delightful experience. Yet that is not enough because we still need the central actors to carry the film if it is going to triumph. Connery is a given performance wise (accent aside of course, but then again who cares when the character portrayal is as sharp as it is here?) but it is Costner as Eliot Ness that shines like the star he was soon to become, it's a magic performance that manages to fuse genuine tenderness of family love with little trips to the dark side in pursuit of making good triumph over evil.
I love that the film is showing how violence and fear affects families, mother and child is a theme that is central to the film's heartbeat, notice how some of the more violent scenes are followed by tender scenes of Ness and his family. The set pieces here are attention grabbing entertainment, a roaring Canadian border rumpus and a smashing roof top pursuit and face off are top value, but it's DePalma gold watching a brilliant Battleship Potemkin homage at the Union train station that takes the cake as the film enters the last quarter. Surely historical facts does not matter when films are as sharp as this one is?. It's frightening, touching, and even witty. So for me at least, the film is 10/10 in every department (and yes, even with Sean's accent).
Footnote: The academy saw fit to nominate Ennio Morricone for his wonderful score, yet strangely he used some of it for the main theme in John Carpenter's 1982 film "The Thing", they must have missed it that time I presume! Must be the genre angle one thinks...

Howard Hawks defined a great film as “three good scenes and no bad ones.” The Untouchables has one of the greatest scenes in the history of cinema, and not just because it’s patterned after the best known scene in Battleship Potemkin; this has actually become iconic in its own right.
This Brian De Palma movie has several other good scenes, and arguably not a single bad one; it does have, however, a couple of scenes that don’t make a lick of sense — some of the good ones, even.
The bat scene, in particular, is a lot of fun, but I still have no idea who the guy is that Al Capone (Robert De Niro) beats the ever-loving crap out of, nor what he did to deserve such fate (I’ve come across a few explanations on Internet, including what my best guess would be, but nothing that stands up to scrutiny).
Of course, Al Capone personally and literally whacking some random asshole to death is as likely as Eliot Ness (Kevin Costner) fatally pushing Frank Nitti (the diabolical Billy Drago) off of a roof — that is to say, not bloody likely; Nitti shot himself dead long after the events of the film (though in a possible nod to the historical facts, De Palma has Ness shooting a hole in Nitti’s hat; according to Wikipedia’s account of Nitti’s suicide, “The first shot fired by Nitti’s unsteady hand missed and passed through his fedora”).
Now, historically inaccurate movies usually make me go ballistic; however, The Untouchables is not a history lesson — if anything, it’s a tall tale with a folk hero (and they don’t get any folksier than Costner) and an archetypal villain (and that’s as close to an answer as we’re going to get to the bat scene question; Capone does what he does For the Evulz).
More importantly, the facts may have been tampered with, but the film’s moral compass always points towards true north, and it knows that dura lex sed lex.