Riri Williams/Ironheart (Marvel)

Ironheart, (Better known as Riri Williams) is the main protagonist of her new Ironheart and Invincible Ironman series. She later took on the mantle of Ironman in a very strange fashion.

Why She Sucks
Note: Some of these issues were fixed in 'Black Panther: Wakanda Forever'.
 * 1) She is a blatant Mary Sue with no personality.
 * 2) Her backstory is rather poorly written, apparently, Marvel attempted to give Riri a tragic backstory to give her more "depth" and more "character development". However, as Literature Devil points out, Riri's backstory is very disjointed and she receives no character growth whatsoever.
 * 3) Like many of Marvel's more recent heroes, Riri's actions are sometimes more villainous instead of heroic. One time she literally stole materials from her school (the Massachusetts Institute of Technology) in order to create her Iron Man suit. Another time, she invaded Latveria. She has also assaulted a board of directors who did nothing wrong.
 * 4) * Despite Riri assaulting Doctor Doom, imprisoning him on the helicarrier and invading Latveria, Doom is for some reason still willing to help her.
 * 5) Riri Williams only exists just to replace Tony Stark, when yet there was nothing consistently wrong with the latter to begin with.
 * 6) * Even worse in that if they really did need to replace Tony with a black teenage girl, they could have just used Rhodey's niece, Lila Rhodes.
 * 7) Her suit's design took a step down from Stark's, barely looking like it was made to battle.
 * 8) She is otherwise a very pointless addition to Marvel Comics, and didn't have a real good reason to become the new Ironman.
 * 9) She is a sociopath and narcissist with a victim complex.
 * 10) She only became a "superhero" because her teacher gave her a sarcastic answer that she wanted to hear so she could "prove her wrong" out  spite.
 * 11) She is self-centered and does not accept her mistakes.
 * 12) She's a creator's pet.
 * 13) Despite supposedly being smarter than Tony Stark, Reed Richards, Bruce Banner and Doctor Doom, she has never managed to create anything Stark hasn't making her intelligence an informed ability. In fact many villains had also managed to create their own Iron Man armours, most noticeably during Armor Wars, making Riri's ability much less impressive.
 * 14) * Also despite being "smarter than Tony Stark", Riri needs to constantly consult her armour's AI just to remember its basic functions.
 * 15) Despite only around for a short while, she somehow manages to develop a cult following of people who kiss the ground she walks on.
 * 16) * This is another example of making characters popular in-universe in an attempt make the audience like them without putting any real effort into it.

The Only Two Redeeming Qualities

 * 1) She is a very intelligent character, and also happens to be even smarter than Tony Stark.
 * 2) She is tolerable in the Marvel animated movie series Secret Warriors, she seems like she’s her own character and her backstory is changed to her being an Iron Man fangirl and she invents like Tony Stark as an escapism when her father passed away.
 * 3) Her character in 'Black Panther: Wakanda Forever' is a massive improvement. In addition, Dominique Thorne does a good job of portraying her.

Trivia

 * Riri Williams is apparently 15 years old in the comics.
 * She is set to make her official MCU debut in the Marvel movie coming out this November, Black Panther: Wakanda Forever and is set to have her own show on Disney+ titled Ironheart.