I actually think the first episode is a bit flat because of the lack of suspense (it's only an exam, after all). I also haven't been following the Nanoha news, so the appearance of Mahou Shoujo Subaru & Teana is a bit of a surprise for me. I guess this is similar to how Raiden appear in MGS2.
Having said that, there are lots of good things in the episode, especially the music and also the new direction with all the girls getting much older. The action scenes are pretty well done too.
I think we are also on track to see Nanoha Jr. and especially Fate Jr. in Nanoha IV
More impression and a few more caps