It's not a BAD movie, but it never becomes a good one. An all-star cast - Paul Rudd, Paul Giamatti, Jeff Daniels, Guy Pearce, Mark Strong, Tom Wilkinson, Hiroyuki Sanada, Sienna Miller, Connie Nielsen, et al. - does what it can with what it's given (not much), but the screenplay and direction made me feel like I was watching a Wikipedia entry.
I highly recommend the book, though; Moe Berg's story is absolutely fascinating, and it's a shame the movie doesn't do a better job of telling it.
EDIT: I changed my mind; it's a bad movie.