The president is much more powerful in the role of blocking legislation than in "gettin'er done". Obama makes for a brilliant president because he acts based on real freaking morals, and has the intelligence to understand multiple perspectives.
We still need to elect Congress critters to initiate the changes - but with Barack, we'd have a president who listens and acts in everyone's best interest, not just his own.
Also - the dude wrote his own speech. We could have an honest, intelligent, eloquent man representing our country.
McCain is saying ridiculous, blatantly false-to-the-point-of-lying things about other countries, and self-admittedly doesn't really know about the Economy. There are pretty serious allegations about his military career being a pile of bullshit stacked on his father and grandfather's navy careers. He singlehandedly destroyed multiple planes and killed something like 17 American Navy-dudes.
He has spittle-flinging rage attacks; cheats on his wife.
Hillary is pretty clearly an 'Ends Justify the Means' kind of gal (at best).
It's hard for me to take anyone else very seriously as a candidate.