Interesting setting and loved the atmosphere of the show, that shows my love for mmorpgs (I play GW2, blade and soul, played WoW, Tera, etc.). Also for a short series, I was never really bored, it was for me, like discovering a new MMO. I liked the angle of living in an RPG world without being "trapped" in a game, the world itself is a game, but that's how it always been. I don't know what else can explain why I liked this anime so much, story-wise I was so intrigued by discovering the setting and how the world of this anime works (like how it would work if it were an mmo) that I wasn't even concentrated in the story. I loved seeing new high-level zones, combat, analysing what kind of classes there would be, professions, new beasts, etc. I felt integrated in the world itself out of my curiosity. Outside of that, radically speaking, I really don't know why I memorize this anime so much.
In short, it's an better version of SAO, with better waifu material.