I've only had a couple of games on Dirty Harry so I haven't had time to really learn the rules. Judge Dredd *looks* a million times better, so there's that! And the Deadworld locking toy is kickass, DH gun isn't as cool IMO.
Dredd has some great modes but the game is pretty much a progression through modes with the only strategic decisions being what modes you pick and when. Lots of great flow. But I understand that DH has perhaps a bit more decision making?