Yea honestly, could be the bitrate but to me they don't look as good as most of the x264/x265 encodes. Also searched through HDBits forum and seems like they also have qualms about the quality, but aren't sure if its do the format itself or just the early stage of the available encoders and lack of options.

Still, the size alone is still a big plus and I'm sure many people would still be interested even with a degrade in quality, and I'm sure it will only get better with time.