I've never thought that myself but it's true that the first half of it is more intriguing. Intriguing would be the right word since it's kinda intriguing like a werewolf gameI hear Death Note kind of stagnates or gets worse or something as it goes on, hence I've somewhat avoided it.
They rushed it HORRIBLY. Seriously, u have a 100 floors dungeon and just skip through them? So much potential wastedI had the same experience. SAO was what really got me hooked on anime. But all throughout the second arc I wish they had continued the story of the first arc.