I think he's a talented actor (great in the Maze Runner), but will he be any good as Pennywise? I've no idea, I know that I was annoyed at the casting of Heath Ledger as the Joker in The Dark Knight and look how that turned out, so I could be surprised at this casting choice.
And, yeah Frodo as a deranged serial killer sounded like the worst casting news ever, another assumption that was unjustified seeing as he pulled it off big time in Maniac.
He won't beat Tim Curry's performance though