Arkham Asylum is the best in my opinion.
Maybe cause of nostalgic but i genuially appreciate how they made an 1 first game set in Arkham Asylum in an horror style.
All phases were memorable(Intensive Treatment, Medical Facility, Penitenciary, Botanic Garden).
All Scarecrow phases, Killer Croc's boss fight were masterpieces.
I also like how this game makes use of easter eggs as part of the Riddler side quest.
Some say this game has age "badly" because of gameplay, but i think this i not accurate at all.
The combat is very fluid and you can even hit 3 enemies at once(the only game with this feature), but the is too easy to lose your combo lol.
The stealth ain't as easy as the other games but there's still gimmicks you can elaborate, the explosive gel is too broken lol.
This game was a hell of a good start for a game series. 10/10