Is this a difficult film?

What do you mean?

I avoided watching it for years because I expected it to be difficult. I finally saw it and was blown away by how much fun it was to watch. The scenes flowed easily into one another, even with 2 different actresses playing the lead, and I found it hilarious and masterful and also fascinating. I hope that in the 3 years that have passed since you posed this question, you've decided to give it a try!

Yes. It's an uncomfortable story. It's most interesting though.

A bird sings and the mountain's silence deepens.

I'm not sure why you ask, what you expect, if you are still curious. But since the question is there, answered twice already, though rather briefly, and the question does make some sense, I permit myself to throw in another perspective:
No, it isn't difficult at all. If you don't make it difficult for you, that is. Buñuel leaves it open to you: it could make you nuts, or just enjoy the many almost hilarious aspects. Just as you like.
The only difficulty could be, if you come 'trained' by Hollywood pictures. Because then it might confuse you more than you can easily take. Just let it flow, develop, watch, take it in, don't expect a 'good' and 'bad' part, don't expect a happy end. If you don't like or don't understand the end, let it rest. Watch it again. Think it over. It makes all sense of the world.