People told you to avoid Demon's Souls? Ah man, you're missing out. you get to see a lot of the groundwork it laid for the future games, as well as how different the lore is.

I can't say it's harder at all. For me, all the Souls games are about in par difficulty wise. In fact, Demon's Souls has a ton of exploits that can trivialize the whole experience. Get on it before the servers shut down!