If there is one thing that I find incredibly attractive (romantic attraction or otherwise) is intelligence. Not just smartness or being knowledgeable, but true intelligence. And Guo Jia has that in spades.
I am going by the DW character here (historical Guo Jia is equally amazing, if in a slightly different way), and there is just no one who comes close to matching Guo Jia. And that includes 'semi-god' Zhuge Liang.
First of all, when Guo Jia does strategy/tactics, he actually implements them step by step. You can see the planning all the way through, how he lures the enemies in, or foils the opponents' plots one by one. It isn't some 'strategy' of random arbalest/ballistae or continued fire attacks. He takes the map, the people involved, the resources required, everything into consideration before implementing his plan.
And he is so polite when doing so. Whereas the other strategists just give orders, Guo Jia always requests for the generals' participation. He is clear in his instructions, ensures the task is fitting to the person, and always minds his 'please' and 'thank you'. Such a gentleman, so it is no wonder that all the generals personally care for him when he fell ill.
Other than his high IQ and EQ, Guo Jia also avoids most other strategists' top failing - arrogance. Whereas the likes of Zhuge Liang and Sima Yi cling onto their "it is all part of my plan" mantra, when Guo Jia retreats, he admits that he may have underestimated the foe. This just makes him stronger the next time. He doesn't claim to know all but instead he continues to learn in order to seek out more knowledge. He knows that there is no such thing as the best, only the best for now.
And finally, he wishes to better others to further Cao Cao's ambition, rather than seeking personal glory. Whereas others might feel threatened by multiple strategists, or wish to take sole command, Guo Jia is always trying to involve everyone in his plans. He tests Jia Xu, before grooming him to take over at his death. He seeks out Xu Shu, and hopes to bring him to Wei. He even asks Sima Yi to join him in revelry so as not to feel left out. Contrast that with the other strategists, and Guo Jia clearly stands out as knowing the power of team work.
The only complaint I have with this character is that why aren't the women falling at his feet? I understand Warriors Orochi has Guo Jia flirting with some (and getting rejected, which makes me think those females are complete idiots), but there aren't any in Dynasty Warriors. How about Zhenji commenting on how Guo Jia is so nice to the ladies, which would totally make Cao Pi pissed off and give meaning to his cold attitude to Guo Jia in the Chibi event? Or Cai Wenji asking Guo Jia for sources of inspiration at which Guo Jia would ramble on about the effects of different types of wine (especially mixed together)? Wang Yi is a little more difficult, but conversing with Zhang Chunhua could be very interesting. I think Sima Yi should be very worried if those two were ever in the same vicinity.
[They stood close together upon the dais - one clothed in radiant royal robes, the other wearing a suave white cape - forming a perfect pair. The lord and his grand commander are indeed a match made in heaven.]
