JK2 had some cool moments, but I didn't find anything as immersive as HL;
I would finger three major reasons:
1. Third person view blows the 'view it via your own eyes' thing.
2. The level design seemed forced at times.
3. One way to make a story seem deeper than it really is to lay down plot lines that terminate prior to resolution. While JK2 may have done this to some extent (the Jedi fighting in the academy) HL did this to an extreme (the leak of radioactive material in the opening, the MIB arguing a point with a scientist behind glass, etc...).
If JK2 had preceded HL then maybe I would have a higher opinion of it. It lacked polish. I hated the long wait for the saber. If they do that again.....who am I kidding, I'll still buy it.
-TPFKAS2S http://www.braglio.org I woke up today and wished for tomorrow I don't want to be like anyone else I woke up today and wished for tomorrow I don't want even be myself