Spoilers below -
For the story more specifically - it isn't until about 20 episodes in that the real crux of where the plot will go towards is known, and it felt like it came out of nowhere. The idea behind the sacred jewel was semi-interesting, but not enough to last the ENTIRETY of this anime's near 200 episode run. First off regarding the sacred jewel - the power increase it gives seems all over the place. One shard seemed like a lot of power, so when about 60 episodes through Kikyo basically gives Naraku a whole half, he doesn't even seem to get much stronger. Really, Naraku during the entire running of the show doesn't seem to make much sense.
He gives up the opportunity to kill Inuyasha and Kagome multiple times, he keeps Kohaku alive for no real purpose (from the perspective of Naraku) in my opinion, and trying to gauge what level of power he has feels impossible as out of nowhere characters in this show (well, Naraku and Inuyasha at least) will receive power buffs randomly.
Also, for the sacred jewel, Inuyasha does not attempt to use a single shard ONCE until episode like 165 to power up. That seemed exceedingly obvious from the get go from all of the different struggles that Kagome and crew had as a source of power to get out of the multitude of near-death situations they encountered. Not only was it not attempted, but the REASON was not at all explained by any characters (it turns out that Inuyasha will basically transform into a complete demon if he does use it, even if it's on the testuaiga and not himself). But, why not address that MUCH earlier?
With regards to the characters, I actually thought they were extremely well written for this kind of show. Kagome, while being 15, is extremely mature for her age but not in an unrealistic way. Constantly self-sacrificing, yet at the same time explicitly jealous (as would make sense) with respect to the feelings that Inuyasha had for Kikyo.
Inuyasha's feelings for Kikyo, however, did not make a whole lot of sense. That is until about episode 130~ or so when their backstory is revealed much more in depth in a two-part storyline. After that, Inuyasha's reasoning feels more, well, reasonable. That doesn't help the previous 130 episodes though, which feel quite obnoxious at times whenever Kikyo is a part of the story.
Kikyo as a character feels rather strange. I would rate the characters of this anime higher if she was written differently. She seemed extremely evil early on when Inuyasha first encountered her after she was resurrected, yet as time went on without any real reasoning as to why, she grew to be more likable. It made her more bearable, yet also didn't make much sense, was it not explained that she was created with basically of the hate she felt for Inuyasha in the last moment of her previous life?
Sango is rather boring as a character, I'd say. The interesting dynamic she has is with Miroku who, well, does not age well at all. Constantly sexually harassing women and also asking female characters as young as basically 12 to "bear his child" (yikes).
Sesshonmaru, Jaken, and Rin had an interesting dynamic. I actually enjoyed whatever they were doing when they were shown on screen, and I almost wish that the development and story of Sesshonmaru and crew was the story rather than Kagome/Inuyasha. The only downside of this trio was how little air time they were given.
One part of Sesshonmaru's arc that didn't make sense and is a reflection of my belief that the author of the manga did not know where the story was going, was his power. It seemed as though Inuyasha triumphed over him early by cutting off his arm while Sesshonmaru was in his big doggy form, yet later on Sesshonmaru becomes extremely powerful and easily overcomes Inuyasha and other adversaries throughout the series that Inuyasha struggles with.
All in all, the show dragged on for way too long and probably would've benefited from resolving the Naraku/sacred jewel plot in 60 episodes rather than 200, then transitioning into differing arcs like other animes of its kind.
