basic personality
Stefan is a very intense individual. Though he often has to cut himself off from his emotions in order to function, every emotion he goes through consumes his entire being. Whether it's love, grief or outrage on the behalf of what's right, Stefan's mind focuses to an unbelievable degree on the subject at hand. He's a very well-mannered, intelligent, stubborn man with the capacity for great things when he doesn't let his guilt get in the way...

dark side
Everyone has a bit of an undesirable "dark" side which manifests itself in a variety of ways. In Stefan, his dark side is in his self-loathing, shame, and inability to let things go. For five centuries he allows the guilt he feels for causing Katherine's demise and his brother's death beat him further and further into self-hatred. It forced him to put a wall between himself and the outside world. Such inclination towards prolonged grieving and shame did quite a number on his psyche, creating a hurtle that he needed to overcome to fully enter a relationship with Elena. He is also overly self-critical and has spells of self-righteousness from time to time.

on friends and love
Stefan makes a very loyal and protective companion. His devotion, once given, is forever and he'll make every effort to protect the people he loves from harm. Because of his fear of his own nature, this need to protect can often alienate the people around him, but it's always done with the purest intentions. He obviously is a strong believer in love and falls hard when it catches his heart, leaving him a mess when the relationship is over.

on manners
On many occasions, Stefan's idea of what a "gentleman" should be is mentioned. Brought up in the world of the rigorous mannerisms of the nobility, Stefan has very clear ideas of what is appropriate and inappropriate behavior for a man. He believes in dressing well is a courtesy to others, that women should be protected under all circumstances, and to never gossip about other people, among many other personal values. These are the rules he lives his life by, guiding him to be that proverbial white knight.

weak?
Stefan's undergone a lot of criticism for his so-called "weakness," a claim I've always been rather baffled by. Sure he didn't take full advantage of his nature and gain the magnificent powers that Katherine or Damon obtained... but they never were important him at all. And is that wrong? No. Stefan had a very defined moral code and he stuck to it, even when it made things in his life difficult. When the easiest thing for him would have been to give in, he stuck it through. Giving into and living in pleasure is the easy path, the road most traveled. I have to really respect being able to hold your ground and stand firm by your beliefs to take that difficult path, the road less traveled. To me that's real strength of character, and anything but weak. Yes, he did let guilt and grief weigh him down much longer than any normal person, but he came out five centuries alive. The pain of it all must have been enormous, but he lived through it. How easy it could have been to end it all... but he didn't. That takes strength too. Basically, my feelings on the matter is that to give up benefits for your beliefs and withstand the daily pressures of bloodlust successfully takes an incredible amount of willpower and inner strength. I can't understand how anyone can look at that and not be impressed.