have noticed that the sentries

are nearly useless when the aliens are attacking.
They are slow to turn, slow to aim, and have crappy range.
It more then once happened that a single builder-alien

took out one of my sentries because it was outside the sentry's range and kept spitting at it.
Also those damn electric bugs

and the large things

jump the sentry, attack it, get behind it, attack it again and destroy it.
All the while the sentry is busy turning around.
Summary: Sentries are slow and have crappy range.
Possible solutions: Speed it up so it can target faster, increase it's range so it can fire earlier, armor it so it can fire longer, or slow the aliens down. Speed/weight ratio is ridiculous for nearly all aliens except

&

Also, concerning strategic placement of sentries:
Maybe have sentries return to the direction they were built in after X seconds of inactivity?
That way they can literally keep an eye on stuff.
With a moderate increase in range this also decreases turning time when there's a target in front of it.
Of course all of this is my perception if the game
Crit?
PS. Yes, I have crappy aiming skills so, I prefer to be a human engineer.