I would wager that English is relatively easy to learn to a basic or intermediate level but as with all languages (maybe not Esperanto, right?) it is exponentially difficult to reach a near-native or native level unless you live many years abroad. It could be a lot more difficult if it had cases, gender, and a difficult verb conjugation system, so thankfully for you guys it doesn’t!
@Paul: Isn’t French much easier than English for pronunciation since there are more useful rules and less exceptions like in English? In other ways like verb conjugation and gender, it is obviously much harder than English. (though that isn’t hard to beat since English verb conjugation is kind of a joke and we don’t have gender)
Romance language speakers should probably have an easier time with English vocab, I would think. Latin words (and French) are the two biggest sources of words in English, if memory serves.