It was our problem with Batman: Arkham Asylum, much as we imagine it was a problem for a lot of you. Rocksteady is looking to fix that in Batman: Arkham City with a "New Game Plus" mode, which ramps up the difficulty and modifies a few things for your second go around Crimeburg. Thugs are meaner, boss fights are tougher and Bats will retain all of his XP and gadgets from the first playthrough.
The difficulty setting for "New Game Plus" isn't customizable -- whether you make it through on normal or hard, the difficulty of "New Game Plus" will be the same. Also, there won't be any counter icons on thugs, but we imagine that won't be a huge deal after you've spent a whole game punching them in the face.