>>24978712BW2 is a horrible starting point for someone who has no knowledge of the series. Not only is it a sequel, but it has one of the weakest and most intrusive stories in Pokemon, precious little exploration, and several early chokepoints that would cause a new player to quit the game. The glory of PWT and the great Pokedex aren't worth slogging through the rest unless you're really into Pokemon,
OP, go for Fire Red/Leaf Green if you can, followed by Heart Gold/Soul Silver. Both are great remakes of their original games that still hold up. (HGSS in particular) BW2 and Platinum are often referred to as the best Pokemon games, but I wouldn't recommend them to a beginner.