This movie is almost 3 hours long. You should know that before you watch it, because otherwise, you might start tapping your toes after awhile wondering when it's going to end, the way I did, and you might not notice what an interesting movie it is, or appreciate the way it slyly unfolds into an epic project.
The movie starts with a quote from Mao ("The Revolution will not be a dinner party...") and then opens onto a scene of class bias, with the poor getting bloody revenge. Juan, the Mexican bandit, dreams of knocking over the National Bank, and tries to befriend dynamite master, former IRA member John to help him. You almost think that this is all the class contemplation you're going to get, when suddenly you find yourself in the middle of Revolution. Very interesting.
Like other movies by Sergio Leone, the pacing is very curious - you'll get a 10 minute scene where nothing really happens, and then fly through a scene that's a focal point for action, and seems totally rushed and underdone. There are lots of super close-up shots of people's faces, which are really interesting, and highly expressive. The music, by Ennio Morriconne, is great as always.
The main oddness of the film is that there are occasional fantasy cuts to IRA John's past that seem completely ridiculous, and don't make much sense. The idea of bringing his experiences in Ireland into play is a good one, and thought provoking, but it's done in such a cheesy, bizarre fashion that it ultimately undermines the effect.
Oh, but the best part - the explosion are fucking awesome. Trains, bridges, churches - this is a big budget kaboom, and it's totally sweet.