Just destroying a 47-ship Klingon armada, all the other ships sent to Vulcan, etc.
Those feats took place after Nero acquired his red matter, though. And off camera at that. We don't even know whether Nero destroyed any Klingon ships for real: the report of such destruction supposedly sends Starfleet away from defending Vulcan and Earth, and the timing is so good this must be a Nero-engineered ruse. Why would Nero bother to involve real Klingons in his ruse, rather than just a false message?
(We do know he is in the habit of sending false messages. The SOS from Vulcan must have been Nero's doing as well, because there was no geological instability when it was sent; the drill only began drilling later on, with the fleet already en route, as we saw when Amanda rushed to the balcony.)
The two times Nero's ship tried to tackle a shielded vessel, she took her sweet time to get any visible results - the first time almost getting rammed as the result. The Narada
was no combatant, apparently, unable to sustain fire or take much return fire. She was simply a big platform to fire from.
Why this would prompt Starfleet to take any
action is another unanswered question. The mining rigs of future madmen should not be a strategic concern to the organization!