Yes, Sword Art Online can be enjoyable, and it gets more hate than it deserves. However, that hate is mainly aimed at the anime adaption, not at the light novel. That's because the anime gives a first impression that it can't fulfill later on - it seems like a battle shounen at first, but that's really not what the series is about. While it worked pretty well for the first arc, it didn't work for the ALO arc, which caused a disconnection (pun not intended) for most viewers. Compare it with Re:Zero, which at no point looked like a battle shounen but more like a seinen, and which works much better because of it.

There are also a few questionable decision on the anime's part. For example, Kirito and Leafa originally saved Tonky during the ALO arc, but the anime skipped this and revealed it only when it adapted the Calibur side story, which for anime-only viewers looked like it wasn't originally planned and only added in to the story in hindsight - essentially, it looked like a complete filler if you didn't know the source material.

There are of course also those that dislike the series because it's popular, but that's no rational argumentation, so I don't address it here.