They're close enough that we think the Doctore replaces Radio.
For many of us, the essential quality of
Play Radio is it's ability to adapt to skipped tracks. This allows a very convenient way to interact with the selection process—especially where the user's attention and means for doing so are limited. It provides an enjoyable way of listening to music using Theatre View and a remote when not in the mood to make a specific selection of choose a predefined playlist. Narrowing the selection by skipping tracks requires little thought and just the push of a button. This is not only very easy to do when consciously listening to the music, but also engages the listener in the process.
From what I can tell,
Play Doctor just creates a playlist. While I'm sure the logic it uses to do so is brilliant, I don't understand how it could possibly be more effective than what I already already do with smartlists. It can't possibly know I like listening to music according to custom styles or what my style categories mean. It could be using external information to search for specific tracks in my collection (e.g., searching for artists it knows match the mood suggested by the words entered), but there hasn't been any suggestion it does anything of the sort. Most importantly, it doesn't seem to provide any way to interact with the selection—other than to redo the list. If this is done with a button press (i.e., new criteria are not entered), then my expectation has to be I'll just get another list I don't like. I could stick with the list and skip tracks I don't like, but why would I want to do that? Rather than it being less likely I'll hear another track like the one I skipped, having to skip a track will just suggest I'm in for the same.
As it stands now, these appear to be two completely different features. I have no objection to there only being one, but only because
Play Doctor seems gimmicky and of no practical use considering the availability of smartlists. It's
Play Radio that provides the otherwise unavailable function of adapting the selection based on tracks skipped. If
Play Doctor is to be a true "successor" to
Play Radio, it should incorporate that feature. When a track is skipped, why can't it simply remove all similar tracks from the list and replace them based on criteria that will attempt to avoid more of the same? That will provide the same functionality as
Play Radio, while still doing whatever it is we're supposed to find useful in
Play Doctor.