If you liked
Sword Art Online
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...then you might like
Tate no Yuusha no Nariagari
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Both characters are transported to an alternate world but only Shield Hero is a true isekai. They also somehow end up as solo players along the way after an incident happened that ruined their lives and team up with a beautiful girl. The differance being that SAO actually has theme of relationships and how our relationship in the virtual world affects the real world while Shield Hero is merely a deconstruction of rpg themed anime in that mc has one of the most powerful weapons in the game but it's too useless to use effectively without a backup.
If you liked
Kiseijuu: Sei no Kakuritsu
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...then you might like
Devilman: Crybaby
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Both deal with interactions with non humans prompted by the protagonist merging with what would in any other circumstance be his mortal enemy. Parastye obviously taking inspiration from the original devilman manga with none of Go Nagai's unnecessarily edgy gore sequences and none of Masaaki Yuasa's weirdly placed sex scenes in the adaptation.
If you liked
High School DxD
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...then you might like
Shinmai Maou no Testament
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Both are ecchi series. Both have a boy who falls in love with a devil princess with red hair. Both are somewhat enjoyable though DxD far outranks SMT due to having better artwork, more interesting character dynamics and cooler powers to boot.
If you liked
Shingeki no Kyojin
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...then you might like
Owari no Seraph
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Both revolve around humanity's recovery from near extinction. Both were animated by Studio WIT. Both are set within a walled off portion of a larger island within which the vampires/titans cannot attack the citizens. I simply prefer vampires over titans as the battles tend to be more strategy based and less going for the nape of the neck. That and the fact that Seraph of the End doesn't suffer from having a plethora of unimportant characters with little character development that will likely be killed off like SNK.