Rey is a Mary Sue.
"Spotlight stealing": Rey is instantly loved, admired and desired by everybody including enemies (BB-8, Finn, Han, Chewie, Kylo Ren, Snoke etc), even when this compromises story logic and character backgrounds. Examples:
-Leia hugs the complete stranger Rey after the death of Han (and supposed death of her son at Rey’s hand) while old friends Chewie and Leia completely ignore each other (JJ already admitted the mistake). This is classic Sue writing: only the Sue’s POV counts, the fact that Leia and Chewie are old friends and the emotional link to Han and always hugged before (carbonite scene etc) is irrelevant;
- Rey takes-over the captain and piloting position on the MF after Han dies (she sits in the pilot seat) – Chewie the 600y Wookie remains the copilot on his own ship of a 19y old woman they just met a few hours before (Sues start at the top);
- Rey the scavenger is sent on the most important Resistance mission to find Luke - but not his sister Leia (who “desperately” was looking for him) or other resistance fighters who know Luke! Rey walks up the island, Luke’s old friends Chewie and R2-D2 mysteriously stay back waiting with the ship (Sue is center). The mission was to bring Luke back, not to send him somebody who he can train there on the island.
-debatable: Kylo removes helmet before Rey, though from the narrative POV it would have made sense that he only shows his face to Han (Sue is center);
- even light sabers and dead OLD MASTERS (Yoda, Obi Wan) call out to Rey, this never happened before with any other Jedi (even “Space Jesus” Anakin) - demonstrating how special Rey is.
"Better than You"/ "Copycat" Sue: Rey regularly bests other character at their game, or rescues them and/or drains competence from them, thus compromising story and character backgrounds. Examples:
- The lifelong soldier Finn looks incompetent and foolish next to Rey (fighting, piloting, languages, Starkiller security and mechanical stuff), is beaten by her, and must be rescued by her many times.
-The main antagonist Kylo Ren, the 30 year old Master of the Ren (and Jedi killer), who is established as very powerful, is beaten, maimed and emasculated (broken saber) by Rey physically and on mind-level several times – all that despite of Rey having no proper Force or sword fighting training. He finally has to be rescued by a deus ex machina plot device (opening chasm) to be save from her.
- Rey constantly advises and bests Han (and Finn) with mechanical and engineering ingenuity regarding Han’s own ship, driving him to angrily leaving the cockpit ("Away Ball") and resulting in him offering her a job quickly.
- Rey also replaces C-3PO as a translator, BB-8 seems completely useless because Rey does all the mechanics and engineering to repair and improve the falcon.