Well to tell you from my own experience, it's a whole lot easier if you already play another instrument. Then it's just getting your coordination down and getting to know your scales. If you can learn your scales on a guitar then you can play anything. You just gotta stay with it and practice a lot. It isn't hard IMO, you just gotta practice.
I've taken classes and at the start, it's really confusing learning basic notes, like D, F, G, C and some other notes, but once you get the drift, it becames easier. My hardness rating has to be 6..or maybe 7. I was forced to take Music classes, and I was like "Fuck! How am I meant to do this" but I got used to it. I am leading guitar player
Well chords help you play rythms and such, but to learn those chords completely you need to learn scales because those teach you notes and how they correspond to each other. Scales help you with notes and a lot of basic and very advanced playing techniques and will help you to understand how chords work.
I'm with Kazmarov. This question is too generic to answer. Playing an open E power chord is a 1. Playing Dragon Force, to borrow that example, or Malmstein, or Yes, or hundreds of other bands or artists is undoubtedly a 10. To make things more complicated, it also differs from person to person. I'm a firm believer that certain people literally do not have the ability to ultimately get to the level of the aforementioned examples. Becoming a virtuoso requires innate talent.
I was actually going to make a similar reply, RT. I was going to say that learning any instrument is more of a matter of natural talent and taking advantage of what you know and are naturally "good at" to help you learn and grow.
On a scale of 1 to 10, guitar is a 1 in difficulty. That's why everybody in the world is an insane guitarist....
Seriously though, it's probably a 10, if not a 15 or higher if you were to shoot for being a guitar legend. It's no walk in the park and it takes 10-20+ years of dedication to get to the level of some of the top guitarists out there. Some have been playing for 50+ years so it would take a LONG time to get even close to that level.