Terrible trade, and not because Lawrie is my favourite player.
Donaldson is essentially a power hitter, and that's the least of the Jays concerns, right now. Offensively, he's not that much of an upgrade, from Lawrie. Lawrie hit 11 HR last season with 70 AT, that would accumulate into 20-25HRs playing in a full season. Not much of a difference where Donaldson hit 29HRs. Defensively, both are outstanding infielders, but I would give Lawrie the edge on this one. Time and time again I heard players praising Lawrie's defensive skills, players from Buerhle to Jeter, saying he's the best 3rd basemen in the league. Those are pretty nice compliments from two of the best defensive players at their position.
Lawrie's has a ton of talent, it's just too bad his intensity level is through the roof, which causes him to be prone to injuries.