Well Lucario appeals a lot of things to me...
I love him so much becasue he is brave, courageous, never gives up, and has a natural sense of justice.
Lucario (and Riolu) actually made me have a favorite Pokemon to be hjonest. I love(and loved) Pokemon, but never really had a favorite, until Lucario rolled up. Then after a while-and seeing Lucario and the Mystery of Mew, I fell in love. Also the fact you can PLAY as him in 'brawl made me get the game in the first place. I would have never bought it if he wasn't in it.
Also, for some odd reason, he reminds me of myself at times. When I look at myself, I (this could be my mind's eye or whatever but...) seem to have a similar body shape to him. Thats what also might be a reason for me loving him-he's so similar in form, and he's just so darn cuuute and perfect at the same time!
And for some reason....(I'm a guy, and I DO say cuute and othe rthings so nyeh)I think Lucario is sexy. I dunno why exactly, but he's...sexy to me.
I've even had dreams where I was a Lucario, and even illustrated some picutres of Lucario (mostly my Pokesona/fursona).
I just love him sooo much!