Personally I think it makes sense that they introduce Will's story concurrently with Lyra's. As much as i love the books, and readers learns to love Will really quickly, it is a little jarring the way book two starts with a unrecognisable character with no apparent connection to the story. I know its a common device, but it is jarring.
In the book Will thinks about when the men started coming to his house to badger his mum for info but its not explained why at that stage because Will doesn't know. In the series that clearly must have started happening at the same time as Lyra's story kicked off and now we get to see it happening in chronological order.
introducing Will before we've even met Iorek Byrnison - in the books Lyra's attachment to Iorek is heavily established and then she compares Will to Iorek on several occasions, allowing the reader to see why she clings to Will. Possibly they plan to show parallels between the two characters as it unfolds rather than through Lyra (because thoughts are much harder to relate on screen in a natural way), before the children meet, so that when they finally do meet viewers can understand Lyra's interest in Will after what happens to Roger.
I think pp are being pretty harsh to be honest. Adaptations are never exact and they can't please everyone. No film or TV show can be as rich and textured as a book, they just can't - they don't have the same storytelling devices available to them, everything has to be visual or spoken, and they are limited by budgets. But I think its really good for what it is. Maybe try looking at it as separate to the books and you'll start actually enjoying it. Or just stop watching and it won't annoy you.