I'm more inclined to be put off by a friend's criticism than that of a professional critic, but I do pay attention to what critics have to say.
With friends, in conversation, I can ask all the questions I want, find out specifics, something not possible elsewhere. My friends also know what I like and dislike and so can tell me in advance what would or wouldn't appeal. I've been put off by, and put many friends off with simple word-of-mouth. It's the most powerful form of advertising after all.
With critics, though I don't take any single review as gospel, it's very easy to get a feel for major shortcomings and issues with a game. I'm a big fan of Aliens, but avoided Colonial Marines like the plague. Would've liked Sim City, but then the online requirement put me off even before the major issues it had. The Escapist review of the last X-Men game (Destiny something) was enough to put me off it.
At the same time, Yahtzee's review sold me on Spec Ops: The Line (since like him, I loathe MMSs with a passion) and Far Cry 3. Probably others too, though I can't name them right now.