I find it interesting that Russia had the wherewithal (S-400 system) to shoot down some of the Tomahawks and the advance warning, but let the raid continue.
They might not have had enough inventory of S-400s in Syria to take them all out, but they certainly could have blunted the attack. The Russians also have a jamming system in place. I wonder if that would have had any effect on the Tomahawk's guidance (see here).