Someone has already bagged the original Star Wars: Knights Of The Old Republic, but KOTOR 2 (as the kids call it, because putting the full name in the title of this post made me realise how absurdly long it is) is honestly pretty great. This is partly because, even though KOTOR 2 wasn't made by BioWare, it has a very similar plot and structure to the first game.
In The Sith Lords you play as an individual known as the Jedi Outcast. You fought alongside Revan, the protagonist of KOTOR, in the Mandalorian Wars, but did a very bad no good thing and now you're cut off from the force and amnesiac and have to decide whether to join the dark or the light, and so on and so forth.
You even get the same asshole robot as before! So if you were like 'I want to play Knights Of The Old Republic again, but with a slightly different wise cracking rogue character' then boy, you should check out KOTOR 2! Seriously. I know I sound sarcastic but I'm being genuine.