The truth is that the central idea was pretty good for a brutal series, but the execution was not at all the best, it became a Gary Stu and then a generic harem.
I remember being quite enamored with the series in the first few episodes, but then things got really boring and predictable. The following seasons didn't improve much, except for the season where they explore more the theme of sentience and the dilemma of when an AI becomes conscious and whether it should be considered life or not, however, that season also fell into the same thing on several occasions.
RE: Sword Art Online: From Triumph to Disappointment