I generally have lowered expectations to mainstream superheroics, but there are nonetheless a few that stand out in my mind:
1. the guide to Wanted. Millar wrote a great story awhich was more or less What if the Secret Society of Supervillains won in the DCU? But Image Comics being Image Comics, they couldn't help themselves and published a really, really crappy guide to go with it. It sucked and I binned it.
2. the ending to The Losers. One of the appeals of this book was its nod to reality: the opening caper by which the team steal a big helicopter was ruthless in its precision and could have come straight from a KGB manual. It was one fo the best thought-out stories I've ever read. But then the ending... a remarkable geological event creates a new island in the Persian Gulf? An oil rig manages to stay upright on it? And a CIA madman claims it as a sovereign country? The series jumped the shark at that point.
3. the involvement of Tom Strong and other ABC characters in the climax of Promethea. Even Alan Moore succumbs to temptation to create a crossover to lift sales. Pah.
And I generally think its a cop-out to depict the president of the US as not being George Bush. The Losers has some grey-haired portly chap who authorised Max to keep the world safe for democracy: the final issues of Millar's Authority had a balding man who had Seth shacked up in the White house with underaged kids as sex toys. Only Ultimates has Bush as President, and they do it well.