There are so many iconic and beloved characters across the three Star Wars trilogies, three main TV shows, countless books and comics, and entire forty-plus year history that to stand out consistently as one of the very best, most recognizable, and most dear to fans' hearts is a hard task. A task that Obi-Wan Kenobi completes with ease.
Obi-Wan is a highlight of pretty much everything he is in and is one of the biggest heroes in the Star Wars franchise. However, just because Obi-Wan is a hero, does not mean he does not have some dramatic deterioration from a character quality standpoint.
Inability To Talk To Anakin
Obi-Wan makes it clear in season seven, after admitting he had an idea in season six of The Clone Wars about what was going on between Anakin and Padmé.
Obi-Wan showed in that conversation from season six; he was never able to talk to Anakin properly about these things fully. Anakin felt comfortable with Rex enough to tell him, but not Obi-Wan, and apart from the Jedi Code, the main reason is likely a combination of Anakin's stubbornness and Obi-Wan's struggle to communicate in such a way, about such things, even though he relates to them.
Hypocritical
One of Obi-Wan's subtle flaws that develop through each prequel trilogy film is the way he acts like a hypocrite, specifically towards Anakin.
He gets at Anakin about potentially losing his lightsaber, despite having lost two himself. He also forgets that he was once a young, overzealous Padawan, one similar to Anakin, and often fails to put himself back in that mindset.
Not Letting Himself Get Attached To Satine
This is understandable from Obi-Wan, but at the same time, one cannot help to think how different, and how much happier Obi-Wan's life could have been if he got attached to Satine and let himself go after her.
By his admission, Obi-Wan would have left the Order had she asked. However, even when they are reunited, Obi-Wan chooses the Order holding back the part of him that wants Satine, something that may have cost him much more happiness, as selfish as it may have been.
Skepticism
There is no denying that Obi-Wan is one of the wisest and most intelligent Jedi of all time, even in the prequels that rings too. However, he is not independent and unique in his perspective, like Qui-Gon, or deep in meditation in touch with the Force and the future to the extent of Yoda.
This helps illustrate the fact that Obi-Wan can be very skeptical. Not necessarily in people, like Anakin, when he has a plan that is a bit less diplomatic than what Obi-Wan prefers, but in the Force too. He refused to believe in Maul's return when Yoda told him, and simply could not comprehend seeing Qui-Gon, or getting the knowledge that he could communicate with him. As he got older, this got better, of course.
Failure To Either Understand, Or Express Understanding Of Other Points Of View
This goes back to the point earlier about Obi-Wan struggling to communicate in a proper, human way with Anakin about feelings and Padmé.
Ironically considering his famous quote from the original trilogy, Obi-Wan struggles to see things from an opposing point of view. This could be in Anakin's feelings as a Padawan, or with Padmé, or when his mother dies, or when he tries to stop Luke going after Owen and Beru, we see Obi-Wan struggle with a comprehension of a non-Jedi point of view many times.
Too Attached To The Jedi Code
That ties into the fact that, throughout the prequels and specifically The Clone Wars, Obi-Wan shows that he, like most other Jedi, is so devoted to the Jedi Code, unable to see its flaws.
He abides by every line of the code in the way the Council at that time interprets it, no matter what happens. The Jedi Council fell due to, in part, its own arrogance, and blindness of which the ancient Jedi Code was a catalyst.
Loose Relationship With The Truth
Obi-Wan's famous "from a certain point of view" quote got a mention earlier and played a huge part in a quality that is prominent throughout Obi-Wan's whole life.
He famously does not disclose the information about Luke's parents, but tracking back to The Clone Wars, he infamously does not tell Anakin about the plan to fake his death. Obi-Wan has a loose relationship with the truth, which he has with, admittedly, good intentions.
Lack Of Faith & Understanding With Ahsoka
For the most part, Obi-Wan and Ahsoka have a very good relationship. They are like two people who like and respect each other and are close by way of being close friends to a mutual close friend (Anakin.)
However, by the end, this all seems to go away. Obi-Wan gets increasingly aware of her similarities to Anakin, which is not that much of an issue, but then everything goes down with Ahsoka getting framed for an attack on the Jedi Temple. Throughout all this, only one person truly sticks up for Ahsoka, Anakin, while the closest person behind him in that regard was Plo Koon. When the two eventually meet again in season seven, tensions are high, more so when Obi-Wan tries to get Ahsoka to talk to Anakin about spying on Palpatine.
& Then The Same For Anakin
This same thing goes for Anakin. It got talked about earlier that Obi-Wan has a level of failure when it comes to understanding Anakin and seeing things through his eyes as a way to communicate with him. But, far worse than this, is the lack of faith Obi-Wan puts in Anakin.
The fake-death incident speaks for itself, but Obi-Wan not doing anything to show his siding with Ahsoka despite Anakin's protests and sound points shows a lack of trust there too. Whenever it happens, it is highlighted through Anakin pointing it out, and despite the two caring for each other deeply, it was a real issue.
Siding Too Much With The Jedi Council
Obi-Wan's Jedi Master, Qui-Gon Jinn was a notorious maverick and someone who did not place the Jedi Council as the utmost authority, and would deliberately and wholeheartedly defy them without hesitation if the will of the Force demanded.
Obi-Wan was not like this. Obi-Wan sided with the Jedi Council on most issues, rarely giving pushback to any orders, only on a couple of occasions really standing against them. His almost betrayal of Anakin's trust, his not siding with Ahsoka, his not going to Mandalore, all of it was at the behest of the Jedi Council, understandable, but, in hindsight, a flaw.