She’s too perfect in that she not only has acquired more skills than ANH’s Luke in less than 20 years or so and in poor economic conditions, but she learns all she needs to know about the Force exactly at the right time.
It seems to me it is a lazy criticism - not understanding the characters in the SW universe, or not thinking through the events in the film itself as a whole (her environment, how she struggles initially to the events occurring around her, the decisions she makes, then how she evolves and adapts through those situations she encounters etc - ultimately ending with her ‘Letting The Force In’, as it were, to not be defeated by Ren in the lightsabre fight at the end of the film).
And here’s the thing: it’s not about adaptating to the environment, because it’s been enstablished with 6 movies that nobody in the SW universe can become a skilled Jedi without training, patience, diligence. Rey, on the other hand… Now, I know people’ve speculated that there might be a reason for her sudden knowledge of the Force (like some sort of training at young age), but it wasn’t even hinted or questioned by anyone in this movie, so even if this were true for the sequels, saying Rey is a deus-ex-machina or “Mary Sue” in TFA it’s still understandable. After all, even with a shared plot, every movie should be able to technically stand on its own.
I disagree with a lot of that JD - for one she hasn’t acquired more skills than Luke has (has she?), and she is clearly not a skilled Jedi or even ‘just’ a Jedi (that may come in the later films?), her first knowledge of the Force is when Han tells her and Finn about it on the Falcon, no?
She is too perfect? Adapting to her environment in which she has grown up… she has clearly struggled to irk out a living as a scavenger and had to learn to fend for herself - but is quite tidy with the staff and bit and kicked her way through a fight (none of which not really Jedi skills). She also knows how to fix things - probably from her life as a scavenger - and has past experience of flying ships - though not leaving the planet atmosphere).
She then nearly crashes the Falcon, later plans to return to Jakku to await a return of family she deep down knows aren’t coming back, runs from Maz’s castle away from where she has the Force Visions after touching Luke’s old sabre - which is her first real introduction to the Force.
The first time she displays abilities with the Force is when she is being interrogated by Ren - she resists his mind probe and is actually able to probe him back from seemingly learns some abilities or skills from this event to help make she escape via the help of a weak minded stormtrooper. This is being a Mary Sue? It may well be a clue for what is to come in her development, or establishing her character as having the ability to use the Force… or a sign of Ren’s over-confidence, arrogance, or even untrained skills - maybe both?
The next time she displays abilities with the Force is where she ‘let’s the Force in’ towards the end of her fight with Ren - a fight she was clearly losing to an injured, yet experienced sabre wielder - though hasn’t finished his own training. And that seemed to me to be the Force guiding her - rather than her having Jedi powers or having more skills than Luke, or being ‘too perfect’… no?