I don't really want to go into too much depth, but I'd like to give an overview of the series and give my opinions it. If you haven't noticed yet there are many negative reviews out there for this anime, and while many of them bring up some pretty fair points, I think some people are being a bit too harsh on it. Let me explain.
Yes it's a popular anime, yes it has flaws, no it's not perfect, but at the very least in my opinion it is enjoyable. The pacing is off, the beginning particularly feels rushed, there were moments where I thought I skipped an episode because of the time skips which made it difficult to really connect with any of the characters in the beginning, and there were some less than stellar instances where it felt like the anime was trying to make me care but failing hard.
Some characters felt to be completely forgotten throughout most of this series too. For example in the beginning we are introduced to a character named Klein who is quickly pushed aside after the first episode and barely seen again and doesn't really make much of an impact at all on the story later on. This seems to happen a lot throughout this series where there might be some emotional moments where a character dies, or something dramatic happens but there is really no emotional impact from it, and the main character seems to not really care that much about it or it doesn't really effect anything significantly.
I really felt this series shined from around episodes 4-13 and I wish they would have kept with that pace instead of rushing an ending midway and throwing something new at us. The second half just felt completely unnecessary and forced.
Pushing the negative aside, I found the overall theme and atmosphere of the series to be great, and being an avid lover the MMORPG genre obviously a lot of things in this series appealed to me. I really enjoyed the idea of being stuck in a game that was impossible to escape from without winning and having real consequences, it really made everything much more dramatic and meaningful in the story. Sadly this quickly goes away midway through the plot.
If I had to pick two of the best things this anime did well for me it would probably be the animation and soundtrack. They both were really well done, and honestly without them being as good as they were this series would have gotten a much lower score from me, and when I say I really enjoyed the soundtrack I mean that I loved it, it was superb.
I think what it really comes down was just the fact that I enjoyed watching it. I can look at the flaws and pick the anime apart pretty easily, but those flaws never really stopped me from enjoying this anime.I really do feel though that it had a lot of potential to be a top tier series, it just made far too many mistakes. Looking at it objectively I simply cannot give this anime higher than a 7. It was good because I found it to be enjoyable, but it wasn't great or amazing.
At the end of the day I watch anime because I want something that will entertain me and keep me interested, and I feel that Sword Art Online did a good job at accomplishing that.