This is a "Read-The-Light-Novel" anime and a slow one, not rushed like many others.
A bunch of amnesic teenager arrive at a misterious world remembering only their names. Right out the bag all of them join the Voluntary Army because reasons and there's the background. After that the story follows a party with absolutely no skill at combat and their struggle adapting to this new world. This is amazing: it gives a whole new perspective of the genre, taking a more realistic look on the situation and even the monsters. I really enjoyed the focus of the show.
Each character is unique and rich in it's own right. It's a short anime and not all of them may appear enough time at screen but I was pretty satisfied. I loved/hated Ranta since he is a good-hearted prick, enjoyed watching the tender giant Moguzo defend the party, fell in love with the cheerful Yume and shy Shihoru (the weakest character IMO) and of course relate to the sleepy Haruhiro.
Art and Animation 7/10
The backgrounds are beautiful. The watercolor style is breathtaking... and you will admire them, like, a lot. There are a bunch of stillness in the show, with our main protagonist explaining current events while we watch these paintings and some not-that-well-drawed characters with no movement. With that said I've never saw so much detail in one butt out of the shonen or ecchi genre. Yume's butt was always on my mind during the whole 12 episodes.
There should be more than just opening and ending in an anime right? Well... not this time. Except for that annoying "waiting lobby" kind of song... yep, the guitar one... I hate it by this point.
Grimgar is slow. There, I made a review in three words. It's rather obvious in it's premise and not that amazing when compared to other shows this season. But it's relaxing like most of these kind of "read the novel" shows and will leave you with hunger of more if you enjoy the genre. I would recommend it... to a few people