I agree I took the SI to level 50 I only got to level 50 since I like the gameplay so much but storywise I did not feel like darth sidious as bioware said when they hyped up the class. The SI story starts falling flat on its face HARD when you leave korriban. Right now I have a level 34 sith warrior and in the sith warrior story I felt like Darth sidious AND Darth vader as a SW. The SW can lie manipulate try and gain more power behind your master's back and all that other stuff in the SI story its the npc's coming up with all the schemes and manipulations and then its the SI going THATS A GREAT IDEA LETS DO THAT!. The only time I felt like a manipulator was on taris when dealing with ashara and then the story does a cop out and does not even give us the OPTION to make her fall to the dark side like the SW can do with their companion.
Hell the sith warrior can lie, cheat, manipulate and they corrupt force users left right and center the sith warrior was doing everything i expected in the SI story. I heard a rumor that the person who wrote the SI story left bioware to finish college if this is true lets just hope the new writer is better. >_> I even have to say that the BH story is better than the SI one.
^ This I rolled a SI after a sith warrior and the part about aszhrya not being able to be converted to the dark side is just Bull. Listen I love the gameplay but in bioware rpgs I do mainly play for the story.