-more and better lighting. As someone else posted, six sconces does not give enough lighting for a 12 x 25 room. Some of things I need are lighting for seeing how to get to your seat, lighting for reading that DVD case, lighting for viewing settings on equipment, etc.
-design seating before construction done. As it turns out, due to PJ mounting, screen size and ridiculously low ceiling (6' 10" - digging down would have tripled costs), I will have to have a riser for 2nd row. Would have been nice to contruct and install BEFORE finish work and carpet in...
-ventilation. I have good airflow in, but the HVAC contractor didn't deal with exhausting stale air. I will have to install some hack to vent stale air somehow.
-lighting automation. Crestron was completely out of my price range, yet I didn't find out about lesser cost alternatives. It's really a hassle to get up and fumble in the dark for the light switch after/during a movie.
-room treatment. In the typical sized basement theater, you can't have too much bass trapping. I wish I had incorporated bass traps into the design. It's a lot more disruptive (and much lower in WAF) to do this after the fact.
We don"t see things as they are, we see things as we are. - Anais Nin