Illogical
Human. This was the one and only word that could possibly be used to describe Jim Kirk. He was sloppy, emotional, arrogant, and annoying. From a Vulcan point of view Jim could be irritating, the type of human to be avoided and yet Spock didn't find him irritating. At least he didn't anymore. Having grown up of Vulcan, while being half-human, Spock felt he understood the importance of emotions, but knew he didn't fully understand the emotions themselves. Jim seemed to have an emotional response to everything, he was the most illogical creature ever to grace the universe, it appeared.
Spock called himself 'Vulcan' and although this fact was only half true, he tried to work by logic wherever possible. Logic and science went hand in hand, which meant logic and Starfleet went perfectly together as well. An unemotional, clear mind was necessary went conducting a star ship. The ability to look over emotions and do what was necessary was possibly the most important thing when in space. Which was exactly why it didn't make sense that Jim was the better captain than him. Jim acting rashly, not always thinking everything through completely, and yet Jim saw what Spock had missed. It was illogical.
Further proof of the over-emotional way Jim acting was the way he was so impulsive. Acting without thinking through the reaction and consequences it would cause. Acting as if life and death were something he could just play with, as though they didn't really matter. Illogical, life was the most important thing in the universe.
Jim didn't even seem to take the job seriously, he seemed to enjoy himself all the time, sometimes even overlooking the seriousness of a situation. He was forever joking about. Spock often didn't see the humour in Jim's joke, and even sometimes wondered what the purpose of the jokes were. He knew, though, that the jokes were sometimes to lighten a situation. Again, illogical, it was often necessary for crew to knew and be constantly aware of the situation, not for it to be lightened.
And yet they say opposites attract and it was all this and more that made Spock love Jim Kirk. Illogical? Perhaps, but he was half-human.