It's not perfect but it's a masterpiece compared to some of the dross on tv (yes Madame Blanc, I'm looking at you ...)
I think people expect more because it's based on Austen but even "proper" Austen can be ropey, such as the 2007 Mansfield Park.
Season 1 was adapted by Andrew Davies who did 1995 P&P (and hundreds of other things) and he's written part of S2 as well, including next week's final episode. I thought the kidnap in S1 was excruciatingly bad and the balloon thing was silly but I absolutely love it. Maybe I'm blinded by love for Colbourne. I do like a man with a troubled past.