Might as well write this out in full.
The campiness
Never really improves, though I found I was noticing it less as the series went on. There is a general movement away from frequent depictions of CGI monsters in later seasons, though most of the magic continues to look a little silly (especially that throwing people backwards telepathically bit) and the music is still trying too hard in most scenes and gets recycled a noticeable amount. Again, I may not be the best judge here since my only other exposure to fantasy in visual media comes from video games and big-budget movies.
The setting
Ahistorical in a way that annoys me. I hate when adaptations of stories with explicit real world settings go out of their way to divorce themselves from that context; it’s a major reason why one of my favorite adaptations of “Cendrillon” is Ever After and why I don’t care for most of the Disney live-action remakes. It’s bad enough that Lancelot isn’t French, but then the show goes on and on about “the old religion” – presumably a pop culture version of the pagan religions of the British Isles plus actual magic – and never once references the religion that supplanted it even in situations where it’s downright idiotic to exclude it…like, you know, weddings, or maybe Arthur’s coronation? I imagine that it must be difficult for Anglos and other Protestants to engage with their pre-Reformation history when Catholicism has such an unavoidable aesthetic presence. It’s all very disingenuous too; we all know what Albion is, and there’s various references sprinkled throughout to real places and peoples, to say nothing of Arthur’s anachronistic battle cry in the finale for “the United Kingdoms” or the show’s last scene.
Merthur
I feel like the internet lied to me, or at least greatly exaggerated how big a deal this pairing is. It may be the emotional core of the show, but I spent almost the entire watch waiting for the other slashy shoe to drop. It sort of did in the second half of the finale when Merlin comes out as a sorcerer as part of a Lord of the Rings-esque sequence with the two of them struggling to reach an impossible destination together, but like Tolkien the show in general feels curiously sexless no matter how many gratuitous shirtless scenes they slip in. Like Frodo/Sam I can absolutely understand why people would ship it, but I’m not feeling it, nor am I really interested in reading magic as a metaphor for queerness in this one situation since so much else is done with it through numerous other characters.
Morgana (and other women)
Had interesting development and motivations up until the third season when she starts smirking evilly in every scene and wants the throne apparently just for giggles. By the time she’s dressing like Bellatrix Lestrange (and the last HP movies were being released about the time this show was, so I can’t be the first person to draw that comparison) she’s virtually identical to Nimueh – anyone remember her? – or Morgause following her first episode where she was actually interesting. Having read Le Morte d’Arthur and some other medieval texts at university I’m aware that looking at women in angelic/demonic binaries could be considered part of the source material, but it gets downright repetitive after a point. Gwen gets to be the overall exception, but her big arc in the last season lets her dip into the treacherous evil woman characterization anyway. Morgana’s death was also anticlimactic to an absurd degree, just a bump in the road on Arthur and Merlin’s last road trip together.
Everyone else
I still have no idea how we’re meant to feel about Uther by the end. His last episode features him as a vengeful ghost who hates everything Arthur is and he’s very much a dick in life, but at the same time he has moments of genuine conflict and sympathy and he does die protecting Arthur…and there’s also that two-parter where he marries and has sex with a troll, haha? Gaius stopped being more than the resident physician and dispenser of exposition sometime around the halfway point. The dragon is also nothing but a dispenser of exposition and occasionally a handy deus ex machina Merlin can call on at will, notwithstanding when Merlin releases him and he goes on a rampage. Mordred is difficult to parse as a whole, though what finally motivates him to betray Arthur and side with Morgana feels cheap in the “here’s this person who’s important to a main character who’s never been seen before and will never be seen again but now they matter dammit” way that TV sometimes does. The other knights are odd in that their level of development is dependent on how much screen time they got before becoming knights of the Round Table. Can anything be said of Percival except that he’s the big one who’s deathly allergic to sleeves?
Overall
Can’t say I’d recommend it, except perhaps alongside Sherlock as a study in (allegedly) subtext-laden British TV shows with large fanbases despite their lack of payoff. It’s just not my style really, though I felt obligated to see it through to the end.