Finally watched it. You've seen all the reviews. It's definitely a major step down compared to the other two.
We're introduced to new protagonists, Sam, a cancer patient, and Eric, a bland, British guy. Besides wanting pizza, there's not much for you to root for or care about when it comes to Sam. Even with her cancer, they should of had it so that she actually did want to make it to safety rather than being completely hopeless. Then Eric was a pretty lackluster character who just followed Sam around the city. He felt like a "filler" character.
If this had been a standalone movie I would've enjoyed it, but being part of the franchise ruined it.