I've recently put some serious time into this game (10% complete, Hard difficulty, hints off, DX9, everything maxed) and am thoroughly impressed with just about everything about it. The graphics, the music, the story, the voice acting, the action, the stealth options, the upgrade and unlock system, the Riddler's puzzles, the optional special objectives... I could go on and on.
Even the challenge on the toughest initial setting is spot on for experienced action gamers like myself. I've died enough times to make me cautious when I enter a new area as well as plan ahead during the battle flow in order to defeat enemies efficiently and safely.
For a single player title, so far B:AC is a near perfect game IMHO.