What episode had the part where David Tennant changes into the new Doctor? I went through the last season he was in but I don't think it was there. Was it in the first one featuring the new Doctor?

It was at the end of the episode called The End of Time, pt. 2.

Yep, he changed into the Eleventh Doctor played by Matt Smith, who I don't particularly like. I do like his companion Amy (Karen Gillan), however.

I wasn't looking forward to Matt Smith taking over as the Doctor, but I was looking forward to Steven Moffatt taking control of the writing. Now the first Matt Smith series has finished, surprisingly I find that I have really enjoyed his portrayal, but I have been disappointed with the Moffatt scripts.

I finally got around to seeing this episode when Matt Smith took over. I really like SMith and even though he doesn't match Tennant's exuberance (honestly, who really could), he does well enough. Karen Gillan is alright as the companion, but they can do away with her fiancee'/husband.

They did away with him once, but the doofus came back.

Yes, yes they did, much to my chagrin. Then they got married and left with The Doctor. Yikes.

I finally saw this. It really hurt it was so bad. So bad.

When you produce a show, have a situation where a character is in a space ship up hundreds (thousands?) of feet in the air but for purposes of the story you need him back on Earth and implement this by just having him fall out...yes, he groaned a bit when he hit the ground but otherwise he was OK - then maybe you need to examine if you care about this thing any more.

What a miserable sendoff for Tennant.