I'm still relatively new to birding, so I find it difficult to know how much of this is my eye changing over time and being better at spotting (combined with having much better camera equipment than I had two years ago), and how much of it is a change in the environment or conditions from this year compared to last.
Cornell has some interesting facts on Eastern Bluebirds:
The male Eastern Bluebird does a "Nest Demonstration Display" at the nest cavity to attract the female. He brings nest material to the hole, goes in and out, and waves his wings while perched above it. That is pretty much his contribution to nest building; only the female Eastern Bluebird builds the nest and incubates the eggs.
Eastern Bluebirds typically have more than one successful brood each year. See a Birdscope article for data from The Birdhouse Network that show this graphically. Young produced in early nests usually leave their parents in summer, but young from later nests frequently stay with their parents over the winter.
Eastern Blue birds are, by the way, quite a bit different from Western Bluebirds, which tend to have a very similar shape, but the males have a darker throat and the females and less contrast on the chest and throat.