This chapter is obviously extremely relative, in the sense that how difficult a language feels depends on a load of factors such as the age when you start learning it (or are first exposed to it), your mother tongue or, even, whether you're cut out at all for that sort of stuff.
However, here's a few points you may find equally useful and disheartening - especially if you're an English speaker.
Learning German is a fucking nightmare. There. I've said it and I stand by it. Like good old Mark Twain once wrote: "Surely there is not another language that is so slipshod and systemless, and so slippery and elusive to the grasp", which is not quite as poignant as another one of his observations: "In early times some sufferer had to sit up with a toothache, and he put in the time inventing the German language."
Quite simply, German is not a language that you can start learning a bit, and then hope to get by and build up as you go along. Unlike, say, neo-latin languages or English, storing vocabulary and attempting to buid sentences around words you (think you) know is likely to backfire spectacularly. In other words, until you master a considerable level, you may find it very difficult to get your message across (apart from simple set phrases, of course), which in turn will make you feel like a retard.
There is a list of about 75 reasons why, aside from languages using different alphabets like Russian, German is possibly the most frustrating, twisted, hostile and complicated European language to learn.
And yet, somehow, there's a category of native English speakers who like to pontificate that "English and German have a lot in common", which is one of the most superficial and laziest statements you could possibly hear when languages are discussed.