Did you feel that way about Anthem or Seveneves? With Anthem, I felt like he had just finished laying the groundwork for an impressive feat of unique world building, which felt a shame to abandon at the end of the book, even though I enjoyed the ending. With Seveneves, I felt the book ended shortly after part 2 finally started to pick up pace, with several new sets of characters, and their dynamics, being introduced right before the end.
The world building is why I can re-read Anathem endlessly. The detail is just wonderful. Every time I finish it I get a feeling of grief knowing that it'll likely never be expanded on.
