While Sword Art Online is one of the more popular isekai anime out there, its protagonist, Kirito, is often cited as being somewhat bland. He's seen as a character who can "do no wrong" and has a harem for no reason. "He's overpowered without being engaging as a character" is a common complaint. Granted, this is how anime Kirito is seen and not novel Kirito, which give more insight into his personal thoughts and feelings.
However, SAO's spinoff series, Sword Art Online Alternative: Gun Gale Online, was received more positively because of its protagonist, LLEN, and how more developed she was as a character.
LLEN does have her shortcomings ability-wise, but in terms of personality and growth, she has a lot more wiggle room than Kirito. Growing up, she was bullied because of her tall height, leading her to become anxious and self-conscious about how tall she is. After learning about online gaming, she tried several different games before finding "GGO," which was the only game that had a short avatar that she liked. Over time, she learns how to communicate with people, including outside of the game, and even receives praise for her abilities from some university classmates. While she wasn't a recluse by any means, as she did have a real-life friend in Miyu, she struggled to make connections with the people in her new environment until she began playing GGO.
LLEN also suffers from social anxiety, which makes playing an MMORPG where teamwork is highly valued rather difficult for her. Contributing to this anxiety could be her place as the youngest of five siblings, having grown up unheard in such a large family. While she certainly isn't immune from being overpowered in some aspects, she still has flaws that she has to try and overcome. Unlike Kirito, LLEN didn't have any outside abilities that would give her an edge in the game when she started, and the fact that her pink clothes happened to blend in with the environment was a fluke. She just wanted to look cute.
While fans are still divided on who is the better protagonist -- and neither choice is wrong -- there are certain things about LLEN that resonate more with viewers on an emotional level. The whole reason she signed up to play was that she wanted to experience being short. It was three whole months before she even thought about taking the game more seriously. LLEN had to learn about gaming from Miyu before she even signed up.
She was a totally blank slate for fans to latch onto and grow with. Many people feel connected to her because many have been a noob before. They've had to learn how to be good at something. Kirito was good at the beginning, and while he made some selfish mistakes at the start, he still had gaming experience before playing SAO. LLEN didn't have that. Viewers could watch her experience what it's like to learn an MMO for the first time and form a much stronger, relatable connection to her because of that.
