Originally begun as a reply to eretria
's request for the character meme that I posted a couple of days ago. But somehow my answer got longer and longer ... ;-) I fear I need to apologize for taking so long to reply. This turned out to be a bit more of a challenge than I first thought; however it also turned out to be a great deal of fun!
So, five ideas/concepts regarding Obi-Wan:
1.) Rooted in Guinness. Being born in the mid 1970s as the daughter of an avid sci-fi fan, I got introduced to SW at a rather young and impressionable age, years before the new movies came out. So, as a consequence, regardless how much I might enjoy and adore Ewan McGregor's portrayal (and good grief, do I adore both Mr. McGregor and what he did with the character;-)), my personal take on Obi-Wan goes back all the way to Alec Guinness's performance.
2.) Keen sense of failure. Whenever I think of Obi-Wan, the image that first comes to my mind is that of Obi-Wan the hermit, who, after long years in his desert exile, has come to terms with his failures, his inadequacies and guilt. There is a strong sense of personal responsibility about him. For him, Palpatine's rise to power, Anakin's succumbing to the Dark Side and the extinction of the old Jedi Order are all part of the same inevitable causal chain that he belongs to and even partly helped set in motion through his personal failings.
3.) Atonement and ruthlessness. Upon meeting Luke, Obi-Wan becomes fully aware that the teenage boy might not only present a last chance at defeating Palpatine and Anakin-turned-Vader, but also a last chance at personal atonement. And thus, he lies to Luke about Vader. The fine art of manipulation is something which comes easier to him than it should actually come to a Jedi.
4.) Always the theorist. Introvert rather than extrovert. While certainly capable of deep, heartfelt emotions ( his spiritual love for the Force, his love for Qui-Gon, for Anakin) he tends to be somewhat emotionally distant, more drawn to spiritual and intellectual challenges/experiences than to physical/emotional ones.
5.) Helplessness and despair. Losing his mentor Qui-Gon shook him to his very core and it took Obi-Wan a lot of time and personal growth to cope with his new role as Anakin's master.