Yes, I agree that this ROM does not do the automatic backlight with as much elegance as other ROMs do. There are some settings in settings->CyanogenMod settings that deal with automatic backlight that you can try adjusting to see if they help, but I am not an expert in this at all.
I think it's under Light levels, check "use custom", and then drop down "screen dim level". I'd guess that increasing the numbers slightly at each level would make the screen brighter, and vice versa. Also note that you can set the soft button backlight levels there, too, so you can dim them a bit when it light levels are low. Defaults seem to have them either full on (255) or full off (0).
(Notice I said "I think..." up above.)