I really want to like the Fifth Doctor. He represents a bold choice to go in a different direction after Tom Baker. He's young and charismatic and more than a little vulnerable, and I must admit the cricket outfit actually works for me (I have my doubts about the stalk of celery on the lapel, though). He also happens to look a little bit like my dad, for whatever that's worth. Not to mention, Peter Davison is really an excellent actor, whereas Tom Baker is just an excellent character, if that makes sense.
So my problem with this era is not the Doctor, it's basically everyone else. Adric, as I mentioned before, is intolerable. Tegan and Nyssa aren't all that bad, but neither of the actresses is particularly talented or likable, to be blunt. Turlough is interesting in concept (a companion who's secretly plotting against the Doctor), but mostly boring in execution. And then at the tail end of the Fifth's tenure comes the single worst companion of all time, Peri Brown. But I'm sure I'll have more to say about her when I discuss the Sixth Doctor.
On the other hand, "Castrovalva" is easily my favorite post-regeneration episode. My understanding (gleaned from the DWO WhoCast) is that it was filmed after the rest of the season, so that Davison actually has his Doctor pretty well figured out by the time the audience first meets him. Compare this to "Robot," in which Tom Baker doesn't quite seem to know what he's doing yet. Also, the inevitable regeneration problems are more interesting than just the "Oh no, the Doctor's unconscious when we need him most!" stuff that "Spearhead from Space" and "Christmas Invasion" are built around. I must confess, I have yet to watch Six and Seven's first episodes, but I'm not particularly expecting either of them to be better than this.