Most annoyed moment: Not being able to beat mission12. I could destroy everything, but as soon as the SOC destroyer got stopped nothing else happened. The transport never moved, and so the mission didn't continue. I was thinking "Major bug!

"
Biggest "I can't believe I did that" moment: Realizing that I had not sufficiently purged my data directory. I had an old copy of the Phobos that didn't have dockpoints

in data/models. Guess I thought that I didn't need to get rid of them, with as many new mods as Inferno contains.
Greatest "shock and awe" moment: the arrival of the Diablo.
My one complaint about the whole campaign is that the dock path on the Vesuvius is too long; it takes an eternity for the supply ship to actually dock with it. Otherwise it's excellent.