I'm not sure all authors wrote in a deliberately obscure way (or indeed in an obscure way at all). The statement is probably true of an author like Apuleius (perhaps the weirdest prose writer of all) and poets, but I think Cicero valued clarity.
As for how hard it was for me (a native French speaker) to learn Latin: definitely hard in the beginning, but I managed in the end. The only language I had studied seriously before had been English, which had seemed, for the most part, incredibly easy. Latin was quite the contrast; unlike with English, learning the basics of Latin demanded a substantial effort from me. Then there came the point where the basic grammatical stuff had become easy enough but I still had to learn the actual idiom, natural syntax, etc. Cf. what Clemens said: "You can learn every Latin paradigm perfectly and still put together a sentence that doesn't reflect idiomatic Latin." That, again, required a lot of effort at first, but a few months of Latin reading worked miracles for me: they brought me to the point where I could read fairly fluently (i.e., really read rather than laboriously decipher with much head-scratching and dictionary-consulting) and write in a fairly (though probably not always) correct and idiomatic way.