The dimensions of Citi Field seem to indicate it will suppress home runs, but Will Leitch talked to the players:

The obvious target seemed to be Derek Lowe, a big-game, big-city pitcher whose deadening ground-ball presence might be especially needed at the new Citi Field, which Mets players who have tried out the stadium say is a "launching pad." (Perhaps the most underreported story of the Mets off-season: That Citi is expected to be a homer-happy park.)

You never know how the shape of the stadium will effect things. However, there's good reason to believe it will not be a launching pad. Shea was never known as a home run haven, and this park is a bit bigger. Since they are built right next to each other, and on the water, both parks are at sea level. The orientation is slightly different, as seen in this photo. Citi also is somewhat more enclosed, so there might be less wind blowing in. My bet is that a few swings in the middle of winter can't describe the park. I'm betting on a tough field for home runs, but we'll see.

Hat tip, BBTF.