TheDudeLebowski: Only played Knight and City up to now. Own Origins, so I'll get round to that one day. Never actually played Asylum, but I think after playing Knight and City, Asylum would seem too simplistic.
Loved Knight, btw!
Asylum absolutely is the most simplistic. Each game following built on the mechanics while increasing the size of the world and making Batman more fluid in control and interaction with the environment.
It is still a fantastic game and feels a bit like... Die Hard. You're stuck on a small island going through a single night seeing the 'battle damage' and toll on Batman. Part of the smaller scale is an advantage too. No other Batman game feels like a Metroidvania as much as the original (it was inspired by them after all). It was my first so I really couldn't give you any sort of accurate advice on whether you'd enjoy it coming off the others or not. I do think it has the weakest story of the main entries, still delivered with top notch production values though.
A minor complaint too as someone unfamiliar with Batman beyond the movies and games, you find loads of Biographies of characters and enemies that make NO appearance in Asylum, but basically spoil their appearances in following games. Hush was an awesome character, imho, with a great intro in City that was... not as impactful having read his reasonings in Asylum in a bio!