While I have read postings stating individuals have had trouble with metadata in general, as far as my own experience, if iTunes has a field for it and data is entered properly into that field, iTunes Match copies all of the metadata.
The real question as you pointed out, is how well does iTunes Match use that metadata if it's used to create smart playlists. From what I have read, the overall experience has been mixed. From my own experience, while smart playlists work fine on computers using metadata they could only be getting via iTunes match, those same playlists either are empty on IOS devices, or are populated in a manner that clearly shows the metadata isn't being read properly.
Here are examples
(1) A smart playlist based on text I had entered in the comments field displays fine on the computer it was set up on, as well as computer #2. In both cases the playlist is reading the iTunes Match database, so songs that are local are mixed with songs available only in the cloud.
This smart playlist is displaying properly on my Apple TV, which perhaps not coincidentally, is the only iOS device that supports streaming.
However presently, this playlist is empty on the iPhone and iPad.
(2) a smart playlist based on BPM over 60 displays on both computers and as with (1), it is clearly reading iCloud. This playlist has not appeared on Apple TV as yet, so I don't know if it will behave identically to (1). However it, too, is empty on the iPhone and iPad.
(3) a smart playlist based on play count, set to show only 25 tracks displays properly on both computers and clearly is reading playcounts specific to each one. Display of this playlist on iOS Devices has no logic to it that I can determine.
Each IOS device does have what appear to be tracks that have been played on one device or another recently, but the list is over 1,000 songs. Setting the music app to display only music on the device will get the track count lower, but that seems simply to be based on how many songs are locally stored. The 25 track limit certainly isn't being honored here.
This issue has been documented by at least one other person who has posted to the board.
My guess is that at this time, play counts unique to each device are not being handled properly, that some sort of aggragate attempt is being made. That there are tracks displayed all all is encouraging though. Some sort of functionality for playlists based on play count clearly is there, just not working properly on iOS devices.
Based on my limited testing, Apple has built in support for playlists based on metadata that iTunes has fields for, but iOS is not currently capable of handling it properly. My guess it that it will at some point (people do use playlists extensively - for Apple to basically kill the functionality for people who "upgraded" by purchasing iTunes Match doesn't make much sense). However if a person were needing full functionality now in order to make a purchasing decision on a metadata "enhancement" app, well Match doesn't seem to be there yet