Okay Bala, your thoughts really summed up it all for me as well!
But I have to agree with the Cristina part, it was great to see her teach Lexie, but in her own way. She can't teach the same way that Burke or Hahn did (although it was great to see the Chief stand up for Cristina to Hahn, because he style of teaching didn't work for Cristina).
And all of the kissing at the end. It was intense! I was wondering who it was going to be during the whole episode, and it was any couple! haha
As for Alex, I don't think he actually had sex with Izzie. I think he just needed her comfort. I don't take is as him using her, but just needing to be loved. And that's how he feels loved.