I recommend downloading the KOTOR 2 restored mod. It implements a lot of content that was cut from the game during development and gives life to the worlds that were rather lackluster when compared to KOTOR.
The restore mod and a few other quality mods and a lot of subtle re-textures and tweaks gives a lot of life to KOTOR 2. So much content that was about 1/2 to 3/4ths finished was cut just so there could be a quicker (winter?) release date. I felt especially burned when Korriban was reduced to a shell of its former self. Copy and pasting the original KOTOR’s korriban with different voice actors and different textures would have been a more quality experience.
For the original KOTOR I recommend a large amount of HD retextures if your pc can tolerate it, and Brotherhood of Shadow, Solomon’s Revenge.