I've only been there once (well twice, but the first time I was too young to remember), and I found the area immediately around the arch kind of sterile, though any place can be photographically interesting if approached with the right vision.

There is lots of interesting grafitti, though, and trompe l'oeil facades on buildings.

While you're there, get to the museum, which has an incredible collection of works by German expressionists, above all Max Beckmann, and some huge Anselm Kiefer pieces that you will never have a chance to see elsewhere, because they would be a nightmare to move.