One Piece is chock full of completely insane weapons & powers. My favourite is this guy who picks his nose, flicks the bogey at you, and then it explodes. The plot, on the face of it, is simple and easy to follow. (Though, it actually runs a bit deeper, if you ever really want to get into it.)
Now, as for your stipulation that it be complete and have a conclusive ending, while the show itself is nowhere near finished, it does divide up nicely into several distinct arcs which all tell their own stories and have satisfying conclusions, while at the same time functioning as part of the bigger plot. To avoid getting burned out on the series, I like to blitz through one of these arcs in a few days, and then leave it alone for a few months, until I really feel like getting back into it.
All in all, while it's far from the best anime around, there are few shows that match it in terms of sheer creativity. It definitely fits a lot of what you said. Especially in terms of dumb (in a good way) & rule of cool.