There's just so much good about tGtBatU. You get some action very early on. Then hardly a word is spoken for like 10-15 minutes. It's a slow build up with much anticipations. It's one of the few movies I know which gives me the same feel as reading a good book. The narration is all visual. The three characters are fantastic. Spot on the lot of them. It has great scenes (Beginning, introduction of The Bad, civil war scene, prison camp scene, desert scene, shootout in the town and the great ending).
Music score is one of the best I've heard in movies. Many people will know two parts of it without knowing which movie its from. That's rare with movie scores.
It's a very long movie indeed and you've got to be ready for it to watch it. I'm not even that bothered with westerns. Like them as well as many other genres. But I watched this for the first time when I was about 12 and really dug it then. Mostly because of Clint. But it has grown better on me over the years.