Yeah, DFL is both groovy and thrashy. It's perhaps one of the most energetic songs ever written, it just makes you want to move and smash the objects around you :hotjump:. Perfectly balanced song, really - heavy and fast just enough, not exaggerated in any element. It slows down for a short while just to kick back with more intensity. It's the kind of a song where you don't notice the lack of a solo.
Not as gloomy as the rest of the album too (not gloomy at all, really), despite the lyrical theme.
The moment when Dave hits the cymbal at 1:21 is already legendary. I love the part from 2:47 onwards as well. The fact that the intro riff is so similar to Overkill's "Elimination" doesn't hurt too.
Of course, like with the rest of the album, I wouldn't mind hearing SDG more, since he's doing awesome stuff there:
It's such a great track for a live set, much better than DNR in my opinion as the intensity of the latter cannot be captured during live performance