This might be a good way to go about it.
ifelse(
Regex([filename (path)], /#ALCOHOL\\Beryllium\\Video\\DVD\\Series\\([^\\]+)\\(.*?)\s+(\d+)\.(\d+)#/), [R1],
Regex([filename (path)], /#ALCOHOL\\Beryllium\\Video\\DVD\\Features\\([^\\]+)#/), [R1]
)
The [R1] is the first occurrence of [Series]. Change it to [R2] to use the Series name from the second listing of [Series], or [R3] to use the Series # (assumed to be one or more numbers), and [R4] to use the [Disc #]. The second Regex's [R1] is the Movie Name when the path contains Features.
You could use isequal() and listitem(), but you'll end up having to do more work to break apart [Series] [Series #].[Disc #]. If you don't need that, and only want the Series or Movie Name:
ifelse(
isequal([filename (path)], \Series\, 7), listitem([Filename (path)],7,\),
isequal([filename (path)], \Features\, 7), listitem([Filename (path)],7,\)
)