This was the most frustrating issue when we moved to Plex from EyeTV.
It was very useful being able to set up “smart recordings” with include and exclude parameters.  Keyword, genre, media type, show name, season, episode name, episode number, description, actors, director, year, channel name, channel number, duration, rating, start time, end time, day of the week, weekdays, resolution and likely more I don’t remember.
I used some very specific settings to re-record episodes with weather banners or other issues:
[Show (contains) “Big Bang” & Season (is) “4” & Episode (contains) “Zazzy”]
Others were more of a wildcard search to catch something we might want to watch:
[Title (contains) “volleyball” & Genre (is) “sports”]
Exclusions helped with errors and omissions in the EPG:
[Media (is) “movie” & Resolution (is not) “SD” & Duration (>) “1:20”]
Regular reoccurring recordings:
[Genre (is) “news” & Channel (is) “5.1” & Start Time (between) “16:55”;”17:35” & Weekday (true)]
Manual recordings:
[Record (at) “10:00” (for) “1:00” & Day (is) “sunday” & Channel (is) “7.1”]       …anyone thinking JIRA?
We’ve come a long way… Or have we?  At this time we may record anything we find in the Guide.  The VCRs of the early 90’s had the same functionality using VCR-plus.  Many of us remember entering a short numeric code from the newspaper guide that set the time, date, and channel for us.  Of course back then, we could also set a manual recording.
We signed on to Plex when DVR was still in beta.  We were not pleased with the bugs and shortcomings in functionality for a project that should have had a very clear set of goals.  Stability has improved greatly and usage has expanded but it is time to remove the training wheels and give us a full, rich set of DVR tools.