The 2nd movie was also based on a book (Lost World by Crichton), so it had solid source material to work with. It also helped that Spielberg was still involved.
I actually really liked the Lost World book, it was really engaging.
The movie was OK, it could have been a lot better, they failed to fully capitalize on the source material.
I never said Lost World was better than Jurassic Park. :) I did think the book was closer to the quality of the original (but never reaching it) while the movie version was mediocre.
I am surprised they haven't released a Timeline movie yet, it seems like a good fit for a mass market movie (plus you'll have all the Crichton fans).