Jeffrey Long’s review published on Letterboxd :
The Purge 3: Election Year is probably my least favorite in the series. I still enjoyed it, but it's the one I can see myself rewatching the least.
It's pretty much just the exact same movie as the second one, with a lot of the same types of characters and even subplots to it, just with a political spin added into the mix. What I loved most about the first movie going into the second is that each of those had a different feel and tone to them, making each one feel unique from each other, where-as this just feels like The Purge: Anarchy, Part 2.
Granted, the new masks are creepy, the death scenes still quite fun and inventive, and the political angle to the whole affair does bring something fresh to the table. Also Frank Grillo returns from the second movie and he's amazing as always.
However, it really feels like Grillo's role was written to be a fresh new character and his addition into that role was a last-minute decision because even though he's the same character he was in the second movie, it doesn't feel like the same character at all). Also, there's no godly need for a Purge movie to be 2 hours long. This isn't some sci-fi/fantasy epic, an hour and a half would have sufficed.
So in the end, I do enjoy this entry, it'll take a lot for me to not enjoy a Purge movie, but it's also the one I have the most issues and complaints about, and can see myself rewatching the least.