The three-way deal, from the Tigers' standpoint, is essentially Avisail Garcia for Jose Iglesias. In regard to prospects, it's essentially a wash at this point. Garcia is an impressive athlete with good speed, throwing arm and ability to put the bat on the ball. At this stage, however, he has yet to develop the ability to pull a good major league fastball with any sort of consistently. It limits his power, and therefore his value. Sometimes stronger players in their early 20s do eventually start turning on the ball, but it's not necessarily a skill that can developed. It's something players, generally, either have or don't have. It does seem to limit Garcia's ceiling.
People seeing Iglesias' .330 batting average with the Red Sox should realize it is misleading. He had a fairly extensive track record in the minor leagues in which his offensive production was been disappointing in Triple A. I have seen him play, but not a lot.  I didn't get a real good gauge from those few at bats and routine plays.

Jose Iglesias: Good field, no hit?

The Red Sox commentators, however, raved about his defense, and you have all been hearing about his defensive skill since the trade, so there is no reason to doubt it. That would make him a big upgrade from Peralta defensively, but it would be naïve to be believe it doesn't hamstring the Tigers offensively.
The good part is that fielding is a constant and shortstop is far more difficult to fill than corner outfield.
Above-average fielders make errors, but they don't go into slumps. Hitting is an up-and-down aspect of the game, for even the very best hitters. The Tigers have the best starting staff in the major leagues and just augmented their bullpen with Jose Veras. Iglesias will help the Tigers' pitching staff, especially Rick Porcello and Doug Fister, who rely on ground ball outs.
The Tigers eventually needed to address the shortstop position after the season anyway, but there is no way general manager Dave Dombrowski would have made this trade were it not for the handwriting on the wall about Peralta's upcoming suspension. It Peralta, 31, were not in trouble with Major League Baseball, it's possible he would have been re-signed as the Tigers' shortstop. He did, after all, just play in the All Star Game, represents one of Dombrowski's better trades (where have you gone Giovanni Soto) and is still in his prime.
There is a lot of focus on Garcia, and the possibility he will come back to haunt the Tigers with the White Sox , a division rival. But the immediate hurt could come in the form of Jake Peavy with the Red Sox. He has tremendous competitive character and it is now very possible the Tigers will have to face him during the postseason.