Amateur is a harsh term to use, The Dark Knight had to cater to a wider audience as an action hero movie. Watchmen doesn't bear that obligation and was able to go all the way with the exploration of the darker side of humanity that's all.
Much as I respect Synder's directions, I can't help but feel that he's rather obsessed with violence and gore (big surprise considering he propelled himself into stardom with Dawn of the Dead).
A lot of on-screen violence in Watchmen could have been off-screen like they were in the comic. I can't confirm this since I haven't read the book in a while, but majority of the "on-screen" violence in the book were shown on characters we've gotten to know (the Comedian, Silk Spectre, Moloch, the guy guys cutting into Rorschach's cell etc). The demise of the thugs and criminals (the butcher, the canteen prisoner) were all done off-screen in the book.