A guy who is predominantly shoot first, who doesn't shoot the ball well. What could go wrong? 
Pretty much the same stats as Bradley last year, except a worse shooting percentage, and that says something.
What is the point of offering Bradley ++ for this guy when he offers nothing more and will probably command a higher payday?
He had a better eFG%, and a much better TS%, which tend to be better stats because they account for 3-pointers and FT (in the case of TS). That said, due to age and defense, I would not trade Bradley for Gallo. I'm all in favor of bringing Gallo here, but not at the expense of Bradley.
To be clear, Gallinari's overall shooting efficiency (50.3% eFG%) and scoring efficiency (57.4% TS%) are
significantly higher than Bradley's (48.2% & 50.3%, respectively).
They aren't really replacement players though. Gallinari provides a significantly more valuable offensive role, given his ability to score off the dribble and get to the foul line on top of being a very good outside shooter. And they play completely different positions.
I wouldn't consider age a significant factor in a comparison here. Gallinari is just over 26, barely two years older than Bradley. Neither is old. And it wasn't that long ago that these blogs were filled with debates over whether Bradley was 'injury prone' so there is no obvious edge to either as far as 'health risk' goes. Both are healthy at the moment.
Also, while Gallinari is by no means an elite, potential all-NBA defender like Bradley, characterizations of him as a 'bad' defender are really off the mark. He's a perfectly adequate, actually slightly above-mediocre defender who's numbers are dragged down by being on a terrible defensive team.
Consider that, DRPM ranks him #30 out of 85 among small forwards. That's not elite. But it is above the median.
Meanwhile, on his team, the 4 point guards, who were on the floor for over 4000 minutes this season for Denver, were Lawson, Nelson, Green and Robinson, who were all atrocious on defense. The first three were ranked 65, 67 & 68 out of 82 point guards in DRPM. Nate was not ranked in ESPN's DRPM ratings (too few minutes?), but he had worse Defensive Box PM than any of those other three.
When you add in that Denver's main rotation also included the terrible defense of Afflalo and Foye, it becomes pretty clear that Gallinari was just an average defender who wasn't going to keep that ship afloat.
I suspect that on a good defensive team, Gallinari would fit in fine and carry his own weight.
It's fair to be hesitant about trading Bradley in a package for him, though. Bradley has his own particular values, including his defense, his improving outside shooting and his being under long term control with a very modest contract. He has a lot of value. And the fact is, Gallinari will be a free agent after this year and, if he stays healthy and has a great year (which is what we'd want), then he'll be expensive to resign.
Gallinari would address many issues with our offense and I'd like Danny to acquire him, but only for the right price.