This will be quick. Klaus falls into two of my oft-mentioned categories, "It's Not for Me", and "Liked for What It Isn't".
I'm not much of a fan of animated features that don't come from Studio Ghibli. Granted, I liked Toy Story 4, which is one of the competitors with Klaus for this year's Best Animated Feature Oscar. Klaus isn't a musical, which pleased me, and it looked good, which was nice. But I was nonetheless mostly uninterested, and I found the main character (voiced by Jason Schwartzman) annoying in the extreme. I couldn't stand to watch him, and he was on screen most of the time.
Klaus is being praised for existing outside the usual Pixar style that is so prevalent today. Like I said, it looks good, a nice combination of current technology and old-school visuals.
So I didn't care for Klaus, but your mileage may vary.