I was just about to say that Escaflowne is probably my favorite isekai! Inuyasha is really good too T∆T
and Kyou kara Maoh too.
As for me, some of you already said it but, I don't like that there is no meaning to the character being isekai-ed. Trunk accident out of nowhere? And why this character and not any other? We need some information on the characters BEFORE they get isekai-ed, or at least, there has to be a properly explained reason as to why they got there. Plus, they have to bring something to the world, or the world has to bring something they could not have in their own world.
Of course, harems. Just, no. And why do they all love the MC, who's usually sooo unlovable??
And same as all of you, I really like the genre, but not how it's usually handled T_T