One of the better "Companion's First Adventure" episodes, and sets up pretty much all of Clara's characterization but still flawed and hampered by the production disaster that was S7.
For me, it’s neither good nor bad - just very forgettable. I’ve watched it numerous times over the years and still can’t really remember that much about it.
I think it’s a good episode mainly for the reason that it’s quite like a classic episode. You could easily place this episode in Tom Baker or Davison’s era. The nostalgic feeling cancels out the fact a sun-god was defeated by a leaf.
I really like the central idea that the potential of a single unlived life contains more life energy and potential experiences than even a life as long as the Doctor's. But being able to substitute a leaf for a person was too abrupt - I don't think they really laid enough groundwork for us to have any reason to expect that would work.