For an actual review, read Pulitzer Prize recipient Rodger Ebert, I pretty much agree with his take and would only offer the following.
First, a brief synopsis from Yahoo Movies:
Michael Clayton is an in-house "fixer" at one of the largest corporate law firms in New York. A former criminal prosecutor, Clayton takes care of Kenner, Bach & Ledeen's dirtiest work at the behest of the firm's co-founder Marty Bach.
Though burned out and hardly content with his job as a fixer, his divorce, a failed business venture and mounting debt have left Clayton inextricably tied to the firm. At U/North, meanwhile, the career of litigator Karen Crowder rests on the multi-million dollar settlement of a class action suit that Clayton's firm is leading to a seemingly successful conclusion. But when Kenner Bach's brilliant and guilt-ridden attorney Arthur Edens sabotages the U/North case, Clayton faces the biggest challenge of his career and his life.
Great cast, great story, great script and deft film making combine to make an engaging film that never preaches and still manages to surprise. I love the themes running through the film, the foreshadowing of things great and small, the choices people make and the recriminations they have to live with. All things considered, one of the better movies of 2007, right up there with No Country For Old Men.