I like Ryan Reynolds (hard not to), and wish he could get himself into better fare and better scripts because he's capable of it. There are the smash hit Deadpool movies of course, which he's perfectly suited to, but also see his nice work in Woman in Gold (2015) and The Hitman's Bodyguard (2017) which show more of his range. Anyway -- "6 Underground" is very much in the same genre as the later Fast and Furious franchise output, and neither much better nor much worse than any of those. Six agents fake their own deaths and make up a Mission-Impossible-type team of anonymous vigilantes who can operate outside the law and take down the worst baddies out there. In this case, it's the standard-issue evil dictator of "Turgistan".

The plot is just a thin device to connect together three or four major action segments. The first and maybe best is an extended car-chase scene through Florence (and the sets are the real thing). Well done, but why do the police and bad guys seem to have an endless supply of cars and cycles to reappear anywhere and everywhere behind them? Since this is a Michael Bay film, don't bother asking. He likes to blow things up and fire lots of guns, so that's what's going to happen.

It's technically well done and injects just enough human interest through the past lives of the 6 to make it all watchable, but I can't see this spawning a franchise.