I've encountered the same problem. A client doesn't want the title boxes (the little yellow text boxes) showing up when hovering over the thumbnails in any displayed NextGen gallery (displayed as an 'Image list').
I found a solution. Edit the gallery.php file found in the View folder under the plug-in folder. You have to delete two entries which apply title displays (one for the image and another for the link). Remove title="<?php echo $image->description ?>" and title="<?php echo $image->alttext ?>" (lines 42 and 44). You can probably remove the display of title boxes in a similar way for other gallery display options by editing the appropriate file in the 'view' folder. But this worked for me. I use 'Image lists' more often than any other display option.
Be warned, when the plug-in is next updated, this edit is likely to be wiped out (overwritten) so you'd need to make a note to remember to update it again manually (after each update).
Let me know if it works for you too.