It is hard to watch the footage without wanting to do something about it. I watched the Vice videos on YouTube a few weeks ago and it was hard to finish especially when they show the doctors trying to revive a guy who looks pretty well dead and caring for minutes-old babies who are still slimy and gunfire can be heard outside. And there are plenty of videos that can be found online of the executions, piles of corpses and body parts, and people being thrown off the tops of buildings.
But I don't see the benefit of getting involved either. Saddam was scum too but that war was a complete waste that got just under 4,500 of our soldiers killed. And like you said, the score-settling is inevitable when the guard changes in those countries. Right now the Shiites, Alawites, and Christians are preparing for the worst. If that country gets taken over by Sunni extremists, they could be even worse than Assad only they would direct their tyranny at religious minorities rather than political dissidents like the Assads have done for decades.
It will get worse before it gets better. Lebanon's civil war lasted 15 years and in that time Israel got involved, Hezbollah was founded, and ~150,000 people got killed. Syria could easily pass that number within the next couple years if this thing doesn't get resolved and neither side can win it.