Not a great game by any stretch of the definition, but if you need something to pass the time, you can do worse.
The various gun positions on the B-17 itself vary in usefulness; some have very limited fields of fire, such as the nose guns or the waist guns; arguably the best turret to sit in is the top-side turret. If one were able to get a better look at the enemy planes, they actually look decent by DS standards, but usually they are just black blobs in the distance for you to shoot at, with little in the name of tactics.
Where the game actually manages to succeed in the sound effects; crew members will generally shout out the direction of incoming German fighters on the clock face, and you can also hear when an engine sputters out at a fixed percentage of health, and the whine of the engines of German fighters swooping by.
It's not a great game, nor is it a good game; it's average in pretty much most respects. But as a budget title, it largely succeeds in the goal of killing time, and you can buy far worse games for the cost. If you go just wanting something mindless with a WW2 theme, you won't be disappointed. Anyone expecting anything deep will be disappointed; this is a mindless time waster, nothing more.