Almost all 1 star reviews for anything are out to lunch. I own a comic & game store, and every 1 star review we've ever gotten are purely mental (some really, really strange) or some friend of a "rival" (we don't really have rivals) thinking that they're doing their buddy a favour by bombing the "competition" (we're not very competitive). They're frankly ALL BS. I'm fine with a 3-star review.
Frankly, I think that 5-star reviews are strange too, but it's what the 5-star system expects (for some dumb reason). IMO if the star-system actually worked, 3 would be considered "good". 4 would be "great" and 5 would be "better than I imagined it could be - it surprised and delighted me".
I wouldn't call this show a 5-star show. I can see how it was to you, but it's a solid 3 (pushing up to a 4 by the final episode, to me). With plenty of room for improvement.
Weirdly the trend seems to be for the 5-star system to be more binary to most people. It's either "I liked it - 5 stars!" or "I didn't like it! - 1 star!" (Which defeats the point of the other 3 stars). But it's not like people are very good at understanding their own feelings about something, far or less agreeing on what the system actually means for us.