When I first saw this film years ago as a teenager, I thought it was way too long, but now and especially since I've been here on the board, I've come to appreciate films a lot more and look for things other than pure entertainment.
I think the film is perfectly paced. Leone had his certain style where he liked to give the audience more than may be needed but it works. He sets up his scenes and plays them out to perfection.
The final confrontation between the three men is a perfect example. He could have easily of shown that in 30 seconds, instead you have the music and the editing all building up for minutes to see who will survive. It's brilliant.