Good for us beneath? No, not especially. In terms of energy efficiency penetrating energetic radiation is pretty poisonous. Still, the typical shower starts very high and therefore its cone of effect is very widely spread by the time it reaches us, the admiring recipients. So, supposing that radiation from a particle with the energy of a ten-tonne truck spreads over 100 square km, your body might intercept something like one billionth of that radiation.  Not nice, but not really impressive. What is more, the higher the interception of the particle, the smaller the proportion of the energy that will penetrate the atmosphere. We would not normally expect to notice the effect at all without suitable instrumentation.

Theoretically such a particle could miss everything untill it initiates a shower a few metres over your head, so that you intercept a large portion of the radiation. That might conceivably be lethal, but as a living hazard it would rank with being hit by a few meteorites. It would take a huge coincidence for the particle to get so low. It would take a huge coincidence for anyone to be smack in the cone of radiation. And particles of such high energy are not all that common, even among cosmic rays.

Of course, such a shower does not announce its own arrival, so if it did kill you, you (or the coroner) might well assume that you had died incidentally of some more mundane cause. A neighbour of mine dropped dead of an aortic aneurism the other day. Another died of lung cancer.  I doubt that cosmic rays had anything to do with either, but how am I to prove it? One might do better to worry about the possibly lethal effects of the shock of winning a bet at the races. It would shock me all right...

Go well,

Jon