I've never read Pride and Prejudice, or watched any other adaptation, and before watching the Lizzie Bennet Diaries I had no clue what P&P was at all, basically (I'm from Sweden). So this is coming from someone who sees the show in a vacuum, for good or bad.
And the show is amazing. Really, really amazing. The actors are perfect for their roles, and in general are so very believable. It doesn't feel like watching characters, it feels like watching actual people. I have to remind myself that it is a show and not real, when I want to scream at the protagonist for sometimes being an a-hole towards the other characters. The characters, while often a bit over the top, are very relatable and you can really empathize with them. A special call-out to Mary Kate Wiles who does her role exceptionally well.
I think the format has a lot to do with it and also fits the story very well. The main protagonists impressions of the other characters, especially those not seen on screen, allow for characters that are at the same time over the top and very believable.
I'm on my third run of watching the show now, and I can tell you, it's not one wasted minute.
This is really a must see, even for us who have no cultural reference for Pride & Prejudice.