From what I've seen, the terrain either shows up broken, flickers or doesn't show up at all on a lot of video cards, the sound stutters like crazy, the tooltips are broken, the game will recommend naming your city "TXT_TWN_NAME_BOX" or somesuch, there's a crash that always happens on the exact same video to 99% of customers, and there are many, many giant memory leaks that make the game slower and unplayable for many people as your game goes on.
I know there's way more, but that's only what I've actually seen in person and have seen confirmed on the Internet when looking up solutions.
To anyone that's gotten this for Christmas and hasn't opened it yet: please look into possibly returning it before opening it and being stuck with it.