I haven't actually watched much Isekai, so I'm not sick of the premise yet.
Buuuuut...I can see where the "I'm a regular Japanese dude transported somewhere and I'm way OP" getting old real fast. Nothing beats the social commentary of One Punch Man for "OP protagonist".
Yeah, most Isekai is a thinly veiled power fantasy wrapped in a harem with a side of escapism. There's just been something about the concept that has really resonated in Japan for the last 15 years or so.
But there are some standouts. Overlord is definitely one, as is Re:Zero and Konosuba.
In the latter 2, the protagonists are VERY much not overpowered. In fact, the premise of Konosuba is basically "What if the isekai protagonist, instead of being OP, was a garbage human being with shit stats, saddled with the worst possible companions?" and played in a humorous light meant to deconstruct the isekai genre.
GATE is also a fun Isekai because it involves a protagonist who is "overpowered" in the other world because he is a soldier in a JDF "special military action" into the other world, so he gets to tool around in a humvee and call in airstrikes on the dragon and stuff.
There's also a genre called "reverse isekai," where a denizen of another world is brought to ours. They often make for humorous "fish out of water" stories, such as in Dead Mount Death Play, Cop Craft, and Ya Boy Kongming.
Other fun Isekai:
Kemono Michi: Rise Up! - A luchador gets isekai'd
Handyman Saito - A repairman gets isekai'd
Log Horizon - Sword Art Online but it doesn't start to suck after the first season
Mushoku Tensei - The title largely responsible for isekai as a genre catching on
