The overgrown vegetation did not really bother me. If Life After People has tought me anything its that plants would take over farly quickly without people to maintain the structures. (of course the shot of Wrigley Field seemed odd since it was TOO overgrown especially given that its located in a densely packed part of the city).
You can always look at the pictures of Pripyat (a town near Chernobyl nuclear power plant) if you want to see what a fairly large town would look like if it were abandoned and not maintained. For example - apartment buildings 24 years after the Chernobyl disaster:
I've seen the trailer for this and the premise looked like it wasn't fully thought through. Since it's another JJ Abrams mystery series, I'll wait for it to get at least to the second season.