The show is masked by plot devices, underlying yet common factors that make no sense at all, and the supposed narrative that our MC, Naofumi Iwatani, is looked down upon heavily, due to him being the Shield user/hero, which disappointingly does not progress further than the stated premise.

Naofumi's character writing on growth is lackluster at best. As the Shield Hero, he is innately challenged with repetitive backlashes from either the royalty, the Sword/Spear/Bow Heroes, or the public, that as show continues, you start to realize how dumb these accusations with no pure basis are. And personally, the insults became laughable and outwardly I lost pity on Naofumi. Naofumi instead became a slave-owner dude who just lost all personality and turned to a lack-of-substance and zero satisfaction in the whole revenge plot due to the characters that are presented too as plot devices, which may I remind you, is THE WHOLE POINT of the story.

Shield Hero's other characters are all underwhelming and again, seemingly used as plot devices to "progress" Naofumi's hatred towards them. Malty or Myne, the first princess and a supposed plot device, falsely accuses Naofumi for absolutely no reason; the King and Pope who very evidently hates and holds a massive grudge the Shield Hero's guts despite who is the actual hero, which has not given any explanation whatsoever; Motoyasu, the Spear Hero - Ren, the Sword Hero - and Itsuki, the Bow Hero, are all complete idiots with Motoyasu and Malty just being Team Rocket from Pokemon; Melty, the second princess, a suddenly lost loli noble who joins Naofumi's party; Filo, a filolial loli creature, who literally just fights for Naofumi; and Raphtalia, a demi-human slave, who I thought was going to be the saving grace of the show yet just ended being a killing machine of a slave-owner with mediocre development.

I also couldn't care less about Shield Hero's world-building (which is one of the main highlights of an ISEKAI) at all , because it was non existent ! The UI of the heroes to look at their HP/Stats/Skills, made the world of Shield Hero look like a damn game, which supposedly should NOT be a game made of NPCs, instead they're summoned to ANOTHER WORLD with real beings. A detailed game-looking UI was close to non-necessary at all, and Itsuki and Motoyasu at the end even mentioned if Naofumi even looked at the "Help/Support" options which could have made Naofumi's travels and grinding MUCH easier.

There was this one specific plot device which I really can't stress enough how it boggled my mind thinking how this show survived. At the unnecessarily long Episode 1, the anime and the King, respectively, supposedly states to the chosen Four Cardinal Heroes (Shield ,Spear, Sword, Bow) that:

1) "When two more wielders of the legendary weapons operate together, it causes an adverse reaction in the weapons. Working separately is highly advised."
2) "It is said that the legendary weapons repel one another by nature. If you work together, it apparently hinders their development"

And here what's crazy, in Episode 19 in the battle of the Pope and even further on, they SUDDENLY needed to work together, completely disregarding said law. . . Even Ren and Itsuki were always together fighting even before Episode 19. Naofumi clearly stated to the other Heroes "Yeah, we can't win if we don't fight together." Now that my friends, actually hurt my intellectual capacity. I don't know if that was just a plot device to force the Heroes to have their own separate parties yet I didn't even felt the presence of Ren and Itsuki's party members.

An isekai's purpose is to immerse the viewers in a vast fantasy world that has lore and world-building and utilize the MC's past life memories and experiences of the real world to make way through the transported/summoned world. Shield Hero fails dramatically in portraying the isekai element and seemed like a shallow fantasy revenge plot, that is very underwhelming and unsatisfying, with a stale set of characters.