-This review is constantly being updated (mostly the little flaws to draw a more "neutral" picture of the whole game-
To begin with: I am not a fan of SAO; the anime was (if at all) OK, the second part of every season sucked hard... but that does not matter for this review...at least not so much.
I've played the game now for more than 40 hours and I am now doing my NG+, therefore I think I am able to help you on your decision, if you should buy the game or save your money for better ones.
To make it "short":

PROS:
+ costumization of everything (+ third person)
+ good gunplay & fast movement
+ japanese game playable with mouse and keyboard
+ replayability
+ not to easy on the 2nd playthrough (because then you are able to play on extreme)... actually sometimes it feels like dark souls
+ great translation work in every section (played in japanese, english and german yet)
+ feeling of immersion (in-ingame friendlist, AI as coop-support, being kicked out of the game, differentiation between game and reality etc.)
+ nice soundtrack
+ open world
+ a lot of named enemies with special loot
+ a lot of loot :>
+ short loading screens
+ performance (Nvidia GTX 970)
+ weapons that differ from on another (not like in borderlands e.g. where everything feels the same)
+ good graphics, fancy colors
+ 4 different areas
+ different bosstypes
+ aim assist system for easier gameplay/ fast enemies
+/- somewhat a mix of borderlands with a (bad) visual novel... but heyy, you can skip the boring parts

Little Flaws:

- Quest-system: you can accept 4 different type of quests, but to do so you have to go to 4 different locations so activate all
- Equipment-system: to equip (or strengthen your gun) you have to unequip it
- the noises of your female mates in battle... well, you probably get used to it before you go insane
- story does not matter; until you finished 75% of the game, it is too irrelevant to watch all the visual novel parts of the game
- tutorial was too long in the beginnig, but you can skip through it as well
- main city seems bit lonely for an "MMORPG"
- auto aim that cannot be turned off ( I do not mean the assistant system in FB) when you zoom in that locks on the not critical parts of enemies what makes quickscoping a lot more pain in the ass.. but it is still fun to do so (the bigger the challenge, the bigger the reward...or so)
- you cannot look straight up or down; therefore, you are sometimes not able to kill an enemy that stays in the sky

BIG Flaws

- AI: The AI in this game is the worst I've seen in a while; not only your enemies (standing there, doing nothing until you hit them & spawning right next to you) but moreover your allies; they are rolling around when are down until they die without even trying to revive you... this can be very frustrating sometimes


TLDR:
So...should you buy this game?
Yes and no. If you put your focus on gameplay itself and are attracted to "loot and shoots" like borderlands, then you should give this game a try; if you want to read a well written visual novel with a good story, you should probably buy Fairy Fencer F Advet Dark Force instead.
I hope I could somehow help you with your question, if this game is worth it; for my part: I am glad that I've bought this game, for me it feels like borderlands in 3rd Person with (AI-)friends and waifus. Therefore it was worth the full price.
If you have any questions, feel free to ask them in the comments below. I will answer them.
Have a nice day,
Reii

After the Patch of March 11th: Still the ♥♥♥♥♥♥ up AI that is not able to revive you even if it is nearby. But hey, Online seems playable now, even if there are not that many players... on the other side: The 4 times I started online with ojne friend, we got a 6 man lobby after one or two games. The hope dies the last, I think.