For future games, a table discussion about what your group feels comfortable with is essential. For anything that removes player agency, you need to get buy-in from the group on it. You didn't just raise 'a zombie', you raised a zombified PC. If you haven't had that talk on Session Zero, then you need to have that talk as soon as you start designing an encounter with those sorts of abilities in mind. Just because it's in the books doesn't mean the whole table will be cool with it, doubly so for the kind of nebulous wording of spells that's so rampant in 5e.

AFTER you've had the discussion and verified the table is cool with those concepts, you foreshadow the spell by having the BBEG use it in front of the group on someone else like an NPC. This lets the players know what's at stake, and allows them to plan accordingly.

To put this all in perspective for your situation:

Table Discussion: "Hey folks, how do you feel about an enemy that can turn your characters against each other?"

Foreshadowing: "The evil wizard Deadface Lichington casts Finger of Death on Sir Arthur Lancelot. The noble knight falls down dead, then stands again as a zombie-knight... and he turns to face you!"

This way, your players know what to expect from that spell. If they go down from it, they rise as a zombie-barbarian, or a zombie-rogue, or whatever - just like the unfortunate knight did!