Talking about the anime again? I actually enjoyed it, but that's probably because I haven't yet read any of the novel for this so I see it as a stand alone as-is. I don't know where it failed to live up to what it could have been. Perhaps it is better that I saw it first. That goblin army CGI though... wasn't even finished LOL. But that's just one part of one episode and I don't care about a mob army.
Now the manga though, yeah this is clearly more thorough. I very much enjoy the manga. Every scene seems to have a bit more impact and detail. The art is terrific. I don't even mind reading about something I already saw and have no desire to skip ahead in the story even if that was an option. I wish it came more often, but you can't rush quality after all.
I do recognize at some point I need to read the novels - well I have a pretty big "do read" list already.