I've played all the way through, and am at the end of the final sequence.
After trying a number of times to finish it, and getting the message about
"failing time-critical sequence", I finally went and looked at a
walkthrough.
Walkthrough says I'm in the right place, and doing the right thing -
sucking spheres out of the columns and firing them at the bit where
what's-his-face is getting ready to escape. However, my spheres don't seem
to do any damage to the panels around him, and every time eventually Alyx
says oh no, he's getting away, and the "failed" message comes up.
 What am I missing??