I'm a little surprised the ever increasing buzz for this show has not reached this here ivory tower, but here I go anyway. I recently caught up with all 23 episodes of this show after hearing constant praise on the ani-twitter and anncast folks about it.
So the whole otaku being sucked into a game world premise has been a cliche for some time, and most other titles do not examine it from a level of simmering ugliness that is made very apparent after the first 12 episodes. Don't get me wrong, the starting episodes remain very gripping, due to the fact the show encourages the audience to investigate the protagonist's death from different perspectives including his own. Note that this is not a show that harps on it's game premise, everything is more or less treated as medieval fantasy after the first episode (The protagonist suffers, feels pain and trauma etc)
A large bulk of the underlying stroyline reminds me of Pigsy from the Journey To The West. Pigsy used to be a heavenly general, whom due to various character flaws attempts to obtain love above his station, and in doing so is punished to experience 1000 mortal lives. Each life is, due to his character flaws, extreme suffering in a greedy pursuit of love, where he is mentally or physically broken. He dies a pitiful death each time, and begs the King of hell repeatedly to end his sentence.
There are parallels to Re-Zero here, but unlike Pigsy's story, is examined from the viewpoint of the human capability of self-reflection. Granted this self reflection takes a long time coming for our Protagonist, and only after being tormented to the greatest of degrees and madness. However that culmination together with a great supporting cast (and in particular a certain character), produces one of the most emotionally gripping episodes I've ever seen, and if you do some research online, broke plenty of fans as well.
Rym and Scott like to point at Evangelion as a source that examines the darker drives and consequences of human behavior. In Evangelion Shinji comes to the realization of his own worth on his own (if I remember correctly), but in Re:Zero it is not so optimistic, the Protagonist required help, and sacrifices along that way.
This show might be the closest this generation of anime fans have that examines such emotions previously looked at by Evangelion. Its style, presentation, and methods of getting to those emotions are different, but I have no doubt for any formative anime viewer watching right now, this will leave long lasting impact.