Both Day of Vengeance and Villains United were created as preludes to an ongoing DC Comics limited series called Infinite Crisis. As preludes, they get the job done: they effectively set the stage for the events currently unfolding in Infinite Crisis, and do so in a reasonably entertaining fashion. As stories in their own right, they're not as successful. Villains United has some nice character development, but it doesn't have much of a plot — it's pretty much just a lot of scenes of supervillains fighting one another, which has a certain visceral appeal but wears thin over the course of 144 pages. Day of Vengeance has a decent plot, but it doesn't have much of an ending. On the other hand, it does have a talking chimp who solves crimes, which covers a multitude of sins.
I didn't dislike these books, but neither would I say they're particularly good. If you're a long-time comics reader with at least a passing familiarity with the DC Universe, you'll probably get a certain geeky satisfaction out of them. Otherwise, give them a pass.
Oh, and in case you were wondering: yes, it's that Judd Winick, from the cast of The Real World: San Francisco.