The first one was the most important though. People already had four years of Obama, and most had a strong opinion of him one way or another. The first debate was really the first time that some people started paying attention to politics this season and were introduced to Mitt Romney. He did a good enough job that it vaulted him into a tie that we've more or less been in since.
The first one was HUGE - it was the most one-sided presidential debate in modern history. Obama was shown to be the empty suit that any intelligent person always knew he was. Obama's supporters know he is an empty suit - but they like the way he is managed by his handlers, so they like it (he is an articulate clean black who can always lean on the race-card as an isle of last resort.)
Romney held his own in the second debate - would have won decisively had Crowley not stepped in and saved Obama from his lies by introducing lies of her own and not letting Romney respond to the most egregious lies from Obama. Also the question selection was pretty biased - the one about 'how are you different from Bush' was as bad as it gets. At the least, Obama should have been required to answer 'how are you different from Carter' during his time. Total Bovine Scatology during that 'town hall.' Only the moderator was able to tilt the playing field so Obama was not completely destroyed.
Romney won the third debate hands down - which is quite a feat when you go against an incumbent in a debate on foreign policy. The incumbent has been immersed in it for four years and has exclusive access to all the important information. Would have been like Obama going against Bush. However, Romney actually appeared to be the more presidential of the two, and displayed a grasp of global influence and level-headedness (if not for a brain-fart on Syria = equivalent to the '57 states)
Obama in the third debate did not impress at all - he was still in the mode of attacking Romney and interrupting like Biden did in his clown role during the VP debate.
I am astonished at how well Romney/Ryan did in all four debates - clear winners overall by a large margin. Put the half-billion smear campaign of Obama into the dumpster forever.
Romney/Ryan are clearly the most intelligent of the candidates by a large margin - and Romney's credentials are sterling. An outstanding resume of competence and due-dilligence. A character unassailable by anyone. The most clean-cut honorable man since the founders.
Obama/Biden showed themselves to be small minded - without a record of any kind of achievement in any phase of their lives - surviving as political operatives only by smear-tactics, fear-mongering, race-baiting, and appeals to radical fringe elements of society. They debased themselves and their offices during the debates and they don't care because the people they appeal to are the very ones who like clown-like behavior, cannot even recognize real achievement, and who abhor polite society.
These debates were epic. HUGE positive outcomes for team Romney. Will it be enough to overcome the power of incumbency and the overwhelming burden of the dependency culture?? Only time will tell.
For the first time I am optimistic we will start turning this ship of state back towards a sane course.
The debates were the largest factor in this turnaround.