I don't think I inherently hate isekai, but the current trend of how it's done in anime is pretty lazy. The main things I don't like:
1. Shitty Videogame Worldbuilding. I mean if the character is trapped in a videogame, fine I guess. But even in what would be regular fantasy worlds that the character either dimensionally shifted or reincarnated into - a lot of these worlds still run off videogame mechanics. They can 'learn skills' and pull up 'stat pages' and have special gamey 'abilities'. I'm not expecting Lord of the Rings here, but at least have the world function more believably.
2. The "isekai" part doesn't matter. A lot of these are just wish fulfilment, and honestly it might as well not have the whole schtick of the main character come from our world. I feel like if you're going to do an isekai, then something should matter. Either the protagonist brings with him knowledge and skills, which makes their journey atypical from your usual fantasy adventure. Which is basically what the Connecticut Yankee does. Nobunaga no Chef is a manga I really like where the main character's modern cooking skills come into play. Or maybe there should be a plot point regarding returning back to their original world. Which I think was nice when Log Horizon does it. But it usually just looks like the main character's isekai backstory is of very little relevance than to provide an easier wish fulfilment fantasy. They usually just acclimate to their world and might as well have been a local all along as the plot progresses. There's some work that put effort in this. El Hazard concerned itself with dimensional travel and whatnot, and maybe trying to get back. Log Horizon did a videogame plot, but the characters were constantly trying to figure out the mechanics of the world, trying to get back was maybe a future goal and they thought about the implications of the various videogame mechanics such as respawning and whether it would have any effect on themselves and whatnot which was cool.
But yeah, if an isekai is going to please me - it needs better worldbuilding and the whole 'isekai-ing' part mattering more beyond easier self inserting.