You have to keep perspective with this one: it's a prequel, not an addition. Check DoestheDogDie.com before going, I spent the whole movie anxious about the cat and having to talk myself back into paying attention.
(Contains Spoilers, to skip, go to last paragraph)
I'd be lying if I said I wasn't disappointed at points. Some of the story beats were under-developed and relied heavily on the cat acting unlike any cat I've ever known. I found myself wishing the cat would disappear (or die 😔) so that the characters could interact with the world more realistically.
Sam (Lupita Nyong'o) is dying of cancer and it makes sense that she needs some help to navigate the apocalypse but... we trade one brown-haired white guy for another. It's NYC, we couldn't cast anymore diverse here?
The monsters are kind of underwhelming. I would imagine that, on day one and soon after that the realization that they're drawn to sound would take some time to figure out. ESPECIALLY in NYC which, the movie reminds us, produces an average level of 90 decibels daily. Unfortunately, we don't get to see the discovery of this information as it happens when Sam is unconscious.
Concerning more info about the monsters, we get a brief scene (inspired by the cat's wandering which heretofore was not an issue, it always found its way back #plotGPS) where we get to see them eating for like, three seconds. It's some kind of vegetation (?) from their home planet, guarded by an "old" monster. It leaves a lot more questions: why is it "old", how could this stuff grow so quickly if we've never seen it before, are the creatures social (seemingly called to dinner by the old one), if so why are there so few in the region of the original story?
Which brings me to the anachronism that this movie proposes. In Part 2, Henri tells us he arrived at the island on Day One amidst CHAOS. In this movie, we see at least 3 nights pass before Eric joins Henri by casually (compared to how it was described in Part 2) swimming toward the last boat out of the city.
Listen, Sam's journey was really beautiful. The monsters stampeding was super creepy. The military blowing up the bridges was a touch of realism (that I wanted more of). There are some really cool moments and good CGI. (Not to mention Nina Simone as the finale number *chef's kiss*)
Truthfully, this is just kinda more of the same, not adding to what we've already seen/loved/learned but just telling another story within the CU. If you take it as such, you're less likely to be disappointed.