Another vote for Q & A, or Greater Than the Sum. While GTTS is technically a continuation of BD, there is enough new stuff that it really isn't that hard to follow.
GTTS was not conceived as a continuation of BD. It was conceived to be: first, an original story of exploration; second, a lead-in to
Destiny; and third, a resolution of BD's dangling loose end of the
Einstein, which is used in GTTS simply as a McGuffin. There's also some tying off of lingering character issues from the previous three books including BD, but mostly in the first three chapters. It's a continuation of the TNG post-
Nemesis series as a whole, not of any single book. Yes, it follows up on some elements from BD, but it also follows up on the information revealed about the Borg in
Resistance, the character of Rebekah Grabowski first mentioned in
Q & A, the B-4 material from
Articles of the Federation and
Resistance, and threads going back to various TNG episodes including "I, Borg" and "The Inner Light." BD is not its primary influence, merely its most recent predecessor.
And though GTTS does resolve some issues and discrepancies from prior books, it's designed to be a fresh start as well, the setup of a new status quo and a good jumping-on point for the series. It fills in the reader on the current status quo and then moves forward.