When I first heard about Black and White through Bulbapedia I was excited about the games, especially given when they announced the features, and the fact that the region of Unova was going to be based on America instead of the usual Japan was something that made me get interested. After seeing Skyarrow Bridge and Castelia City revealed I started to love the awesome graphics and wanted to get the games as soon as they came out in English.
When the Pokemon were still getting revealed I was impressed by all the cutesy ones (like Minccino, Emolga and OSHAWOTT!!) and all the strong ones too, like Reshiram and Zekrom. The whole yin-yang theme going on with the game was a fun but interesting concept that made me want the games so badly. I tended to read the B/W news a lot so I knew all the spoilers before the games were released.
The fact that no old Pokemon were included until post-E4 made it that more interesting cos I loved the designs of most of the Unova Pokemon and it was sort of a smart move taken by Game Freak, who wanted to remind players of the R/B/Y days.
When I started my playthrough of Black in October 2011, the story and the amazing environment captured my heart, and I loved the new Pokemon so much I wanted to try them all. Unlike most people, I actually liked the designs of most of the "odd" ones (Klinklang and Vanilluxe especially) and I also liked the character designs too, especially Elesa, Iris, Bianca, Cheren, N and the protagonists (Hilbert and Hilda).
Now that I've also played Black 2/White 2, my opinion is that I still liked B/W story-wise but features-wise I liked B2/W2 better. Black and White would have to take the cake for the most epic story in the entire franchise of Pokemon, the new Pokemon appealed to me a lot (I have never found so many favorite Pokemon in one region!) and the basis of Unova was what made the 5th Generation so unique. X & Y is going to have to do a lot to top the awesomeness of Black & White.