I think critics have given out praise far too easily for HotD.
The issue I have had with HotD is how insular it has been. GOT was so huge in scale and scope with multiple storylines, extremely interesting characters and set in diverse parts of Westeros. It feels like HotD has been set in a dark room with characters that have lacked personality. I hated it when they switched actors, especially since Milly Alcock was one of the only ones with a bit of pep (loved her returning from the boar hunt). I haven't read the source material so cannot comment on that.
Having said that it has started to come into its own now, and I really enjoyed the final episode. It looks like the world is finally about to open up with a lot more at play, so I'm pretty excited about season 2.