My very brief take, since all my more specific issues with the film have been rehearsed at some length by others already: Watchmen is best thought of as the cinematic equivalent of a Super Powers action figure. As a freestanding work of art, it has negligible intrinsic value… but that’s almost beside the point, because it does the work of serving as an imaginative link to a beloved narrative.
This is obscured somewhat by reviews, which by their nature aim to answer the prospective moviegoer’s question: “So, is this a good movie?” Probably not, but really, who cares? Why would you want it to be? We already have an excellent work of art called Watchmen, and it was done some 23 years ago by Alan Moore and Dave Gibbons. It relieves the Zack Snyder effort of any obligation to be a great film. Wouldn’t it be pointless if it were? “Hey, let’s do that again, exactly, but with actors instead of drawings!”
I’d say ignore any good reviews that purport to consider Watchmen as a film in itself — these are silly. Ignore the bad reviews as well — these largely miss the point. Reread the original comic, which deserves its reputation as a brilliant and seminal work, and then enjoy the movie in the spirit of an accessory.
By the by, everyone’s seen the Saturday Morning Watchmen spoof cartoon, yes? High-larious.