Here's a screenshot from my inbox:
Having only the Q number is not very useful to coordinate and prioritize contributions to Wikidata, and it defies the many email filters that I have set up to handle incoming messages on topics I am interested in (not just for wiki stuff, but in general).
So I suggest that users should be able to get the labels as well, at least in their default language, but ideally in a way that could be configured by language.
The same goes for on-wiki notifications, as discussed for reverts at https://phabricator.wikimedia.org/T116762 .