These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Alternate Character Interpretation: Noumi. Was he always a nice guy with a whimsical side before getting corrupted by Brain Burst, or is his new personality a result of brain damage when he loses Brain Burst?
Also, was he always bullied by his brother, starting his descend into Jerk Ass, or did he only get bullied only after he installed Brain Burst?
Black Lotus' theme, "Alert Sign", first heard in Episode 5. During her fight with Yellow Radio in Episode 11, it gains a kickass beat that firmly cements her reputation as one of the best Burst Linkers currently in existence.
Haru's theme, "Silver Wing". This theme is the immediate indication that Haru is about to mess you up, try asking Noumi... oh right you can't! He doesn't remember it anymore!
Broken Base: There are some who disagree with Kuroyukihime, and feel that staying at Level 9 and refusing to risk it all for a prize that doesn't seem worth it is the sensible decision. This does get a bit easier to swallow once the negative effects of the Non-Aggression Treaty are revealed. Also, most of the other kings are secretly plotting against eachother to reach level 10 anyway. Kuroyukihime is just the only one being honest and upfront about it. Haruyuki also has a monologue about how a game shouldn't go on forever.
Yen Press deciding to drop name suffixes from their translation of the novels. Some argue this affects characterization, specifically having Haruyuki refer to Kuroyukihime by name rather than just "Senpai".
Which has repeatedly been debunked by the author, especially considering that Snow Black came from an unhappy, loveless family. Although many fans are convinced Kirito must've been involved in the creation of Brain Burst somehow.
Game Breaker: Considers himself one of these in-universe after Dust Taker starts combining Silver Crow's flight with powerful ranged weapons.
Les Yay: Snow Black and Megumi. It's implied that Megumi seems to have feelings for Snow Black.
Like stated above, Chiyu had scrappy status throughout the Dusk Taker Arc and only got better after the reveal of her Fake Defector gambit.
Haru, for some, is hated for being a whiny protagonist. Even though unlike a lot of whiny anime leads, he DOES grow out of it.
Screwed by the Network: A variation. Reki Kawahara has gone on record stating that the reason there aren't any plans for a second anime season is because the studio (Sunrise), is too busy making Love Live!, which sells by the buckload. There is hope however, consider Kawahara (the author), his editor, the execs at Dengeki Bunko, the staff at Sunrise and of course, the fans ALL want another season to happen. So it may just be a matter of time.