Bioware's games are famous for their morality. Actions have consequences; characters die, plots are revealed, villains are vanquished, the innocent saved. Unlike other Bioware games, The Old Republic won't have the option of saving and redoing a section if you mess up. If someone dies in a TOR storyline because of something you did, that person is dead. Congratulations, you jerk.
This morality play in Bioware's games is one of the main draws for me. Dragon Age: Origins has one of the greatest decisions I've ever had to make (I won't spoil it, but yeah, my dwarf took the deal). I literally agonized over it for hours before I finally made my choice. Then I promptly loaded a previous game and reversed course because I simply couldn't live with what I'd done.
TOR will afford me no such luxury. I'll need to make decisions on the fly and there will be no save point to return to. I'll have to live with that decision, good or ill, and all the havoc it may or may not wreak. In short, I'm going to be a total wreck when it comes to a big moment.
As such, I'm going to provide a short guide about how to make awful, terrible decisions and be a bad guy in Bioware games. I find myself becoming emotionally invested with my characters and agonizing over choices that may or may not affect their companions and storylines. Here's a quick guide on being evil in Bioware's epics.
1) Play through as a good guy once. Can't stress this enough; you'll never know how depraved you can be unless you're a hero first. That peasant you saved in the village? What happens if you blow him off the second time? For TOR, this may not be as applicable since each class has separate storylines, but at least you'll get to be a good guy first. Makes you feel warm and fuzzy.
2) Make your villain nonhuman as possible. Or if you actually like aliens (like me) make it as human as possible. And ugly as sin. The less you identify with your chode of a character, the better. Makes the tough decisions that much easier.
3) Revel in your evil. Go out of your way to make horrific choices. Make a mini-game of being as evil as possible and you won't really think too much about the bone-crushing emotional baggage that Bioware is famous for dumping on their villainous players. Seriously, Jade Empire has a villain decision at the end of the game that made me weep. MADE ME WEEP, PEOPLE. I had to leave the room because I couldn't watch what I'd done.
4) Play against type. My first two characters are going to be an Imperial Agent and a Sith Inquisitor; the Agent I'm playing as James Bond who just happens to be an Imperial; loves his government, kills anyone that threatens their lifestyle, and fights for his Emperor and Chiss everywhere. The Inquisitor I'll play as an honorable villain, sort of like Erwin Rommel. My bad guy? Oh, it's going to be a Jedi Knight. He'll be pompous, arrogant, vicious, bloodthirsty, and xenophobic asshat. And he'll probably be a human. Evil little buggers, they are.
5) Take a breath. If you get as emotionally invested in your characters as I do, then you'll need to take a deep breath before you jump off the bridge to Evil-Town. It's just a game, and dammit, since it's just a game those aren't real tears because dammit tears mean you care and you don't care because it's just a game dammit! Ash, why'd you do that?! Tali would never leave me!!! *whimpers and cries*
Long story short: don't identify with your villain, play the "how evil can I be" game, play against type, revel in your vices, and remember it's just a game.