I don't have much problem with grenades as alien, as long as I am there when the grenade is thrown. The problem is when the grenade is laying in a hall or something, or thrown right before spawn, and I run into it unawares. However, it seems like this is reasonable, that if a human is lucky/skilled enough to anticipate exactly when an alien will walk by or spawn, he should get the kill. Plus, the grenade is one of the few things that is reasonably priced on the human team @ 200 credits, and considering you can kill a dretch and still not get your money back, it is pretty balanced for cost vs power.
I do think more aliens need to pay attention to their sound. I play with headphones and listen carefully, so it is never a problem for me. It was a problem though for two tyrants who got stuck on each other while retreating on karith and didn't hear me drop a 'nade in their escape route... :wink: