English is as hard as any other language. A lot of factors affect the degree of difficult it holds. It's accessibility, wealth of resources, and greater "need to know" in the professional and education realms certainly serves as a motivator to decrease its difficulty. Need is the most powerful motivator out there. People who think (or literally do) they need to learn English generally learn it more easily, because that priority makes a huge difference. This is why a lot of people learning languages as a hobby never learn the language. There is no need, and therefore there is much less motivation for doing so.
I think Northern Scandinavians (i.e. Swedish) would have the easiest time learning English, followed by Germans. English grammar actually was influence by and co-evolved at least party in lockstep with Scandinavian languages, so a fair bit of their native intuition applies to English. You're, largely, just swapping out vocabulary (for the most part). A Russian person learning English is learning the same language, but it will be much more difficulty because they are not coming form a native language with this amount of built-in advantages.
Vocabulary is easier to assimilate than grammatical structures, IMO. Plus, those languages have many cognates with English, anyways.
How easy the language is varies from person to person, and depends on the specific situation and motivations that person has when learning the language.
Crazy spelling aside, I think that English is a fairly easy language to learn. Katarina mentioned crazy articles (yes, but the same goes for most - all? - Romance and Germanic languages), pronunciation (hmm, it's much easier than French pronunciation, at least for me), tenses (well, but there's virtually no conjugation to worry about, plus you don't have to use all the tenses in order to make yourself understood), and spelling (there, I must agree; whoever invented the spell checker should be given a medal). Also, remember, English has no cases (except for pronouns), and virtually no grammatical gender (except for what's biologically determined: a female is a "she," a male is a "he," but an inanimate object is always an "it," unlike in plenty of other Indo-European languages).
