I agree, could have done with another year in development. I think there's 2 main reasons it's turned out like this. 1st, budget reasons, another year in development might not have been feasible for them, we all know the trouble SE has had before, and 2nd, I think disk space. They basically filled it up, and I feel there are a few places where it seemed they just cut stuff, either because it was too long, or wasn't fully realized. This all really ties into the rocky development that it had.
DGMW, I love what we have now, and I think with DLC, they can make it into something fully realised, flesh out some of the story bits that feel rush, and add in some places that feel missing (Tenebrae).
I just can't shake the slight disappointment I have in my chest, even though I really enjoy playing it and finding cool things. It just feel slightly off...
Edit: If anything was cut, either because it didn't fit or was undeveloped, I hope we get all that added in as DLC. As someone said above me, if they're really listening to the fans, which they have done so far. They'll priorities adding in, or back in, the stuff they couldn't get in due to time constraints.