Kira Kira's Kirari route has some fun twists in it, Rewrite has a really batshit twist that sets up the final route even by Key "true end" standards, "No, Thank You!!" has plenty of twists throughout all of the routes and also adds additional scenes on replays to further develop the story on top of being the best BL game available in English, Kikokugai has an interesting take on little sister heroines plus it's Urobuchi at his Urobuchi-est, there's Ever17 and Remember11 if you want stuff from the Zero Escape writer, and Hatoful Boyfriend and its fandisc both have some really interesting and shocking material near their ends (no, really).