In Arkham Asylum, the Riddler didn’t convey much of a threat; he was more of a “casual distraction” from the mission at hand. However, in Arkham City, he’s going to be quite the formidable opponent.
According to IGN, when previewing the title, they experienced an elaborate “death trap” placed by the Riddler. The trap involved a hostage suspended to the ceiling above an electrified floor, which would kill Batman in an instant.
Rocksteady Studios even stated that in the first game, the Riddler’s job was basically “verbally abuse.” But, this time around, he is a bit harder to beat and he had hidden around 400 Trophies around the city.