It looks like you're new here. If you want to get involved, click one of these buttons!
There was some debate before the game released about how replayable the game is, ie. by my definition how fresh and interesting a second or third character is.
I have played 4 characters past level 20 on the same faction. I have played to characters past level 30 and one past level 40.
The replaybability is terrible especially if your first character was a stealth class that can skip fights. Every single character will wind up doing the exact same quests in the same area almsot 90% of the content will be shared extactly the same. The only 10% difference is the class quests of which you will do roughly 1-2 per level after leve 15 o 16.
If you solo the game and stealth past some fight you must do almost every single quests that exists. If you solo and don't skip you will need to do about 90% of the quests.
Obviously if you grind instances you may do less or possibly none at all.
The only variation that exists is in light/dark side choices/companion reactions. And in the end simply by playing one light side and one dark side you have basically seen all there is to see except the small portion of quests that is the class quest (which is far too slow to develop to justify griding through the same quests a third time). Compaion reaction is novel and all but in the end only matter from a roleplaying perspective anyway as gifts is the way to go if you have seen it all before. And frankly that is extremely meager picking unless you are really into the role play part.