I found a picture I took of the Chicago skyline from Adler planetarium in November 2002, just a few months into college. This weekend I went back and got the same shot, layering in the developments that have been built in the interim.
Here's the resulting gif:
What's interesting to notice is that from this vantage point, the difference doesn't seem huge. But that's because a lot of the development happened in Streeterville (not pictured, except for One Bennett Park), the West Loop, and Wacker Drive, which is obscured by taller buildings.
But if I come back in 2030, the differences will likely be significant with a complete Bennett Park, Vista, Tribune Tower, One Chicago Square, etc.