It's largely because it presented itself as a soft reboot of sorts, so when you got Pokemon that are similar to Gen 1's Pokemon, then you get an idea that it would feel a little different then the other regions (which is ironic, being a soft reboot and all).
And it's not just that, but also the story of BW and a lot of the characters are different too. You don't end the story with you becoming the Champion, Team Plasma's initial goal was to seperate Pokemon and people instead of some world domination goal (that is, until the end where it was revealed that Ghetsis wanted to rule Unova), the player characters and rivals are older than usual and being a region based on the USA, it means that even the towns and cities have a different feel to them compared to the first four generations.
