Adam Eaton is a good player, a high-OBP guy with doubles power who plays his tail off all the time, but he might not fit what the Nationals really need. He’s not a center fielder, although he has played it and, I’m sure, would volunteer to go play it again. His defense in right field has been consistently outstanding -- by advanced metrics, Statcast data and scouting evaluations -- but in a season in center in 2015 he was awful, and that dropped his value to the White Sox by about two wins. The Nationals appear ready to plug him in there, but I think Bryce Harper might be the better option in center, with Eaton providing more defensive value in right anyway.
I think this would be a huge overpay for Eaton the player, but the Nats are also acquiring the contract he’s already signed to: three more guaranteed years and two option years for $38.4 million total if both options are exercised. If he’s even a four-win player, which he has surpassed in his two full seasons as a right fielder, that screams "bargain" for the Nats' budget and does a lot to justify the high price they paid in prospects.