Ever since I got the Phantom Menace Visual Dictionary back when I was seven years old, I've always liked Plo Koon. I thought he was awesome looking with his mask and weird skin. I liked him even more when Jedi Power Battles came out, and he was one of only several Power of the Jedi figures that I bought.
When the Attack of the Clones toys came out, I was so excited to have Plo Koon be the fourth figure that I got from that line. I was psyched to see him in the movie wielding a lightsaber. (Alright, it was only for two seconds, but it was still cool)
I was kind of disappointed to see Koon die in Revenge of the Sith. I would've loved to have seen him fight back, or maybe even survive Order 66. I think the Plo Koon had a very unique design for an alien, and I would love to see a novel or a comic with him as a main character. I've always felt that he hasn't gotten as much love as some of the other Jedi Council Members (i.e. Shaak Ti, Ki Adi Mundi, Saesee Tiin)