Pokémon Black Is the last hurrah of the old gameplay style. Days before party XP and when the encounter rate was still turned all the way up.
The thing that makes this Pokemon games stand out compared to older and New Pokemon games, Is it tries to go back to the first one, with you only having access to 156 pokemon before post game.
Which on one hand is a very daring and interesting decision, but in my opinion I enjoy all the mix of and teams you can make with 400 different Pokemons in a game, and this just not hit the spot.
But the pixel art is so good on the pokemon's, it is one of the few games where they feel alive because they are constantly moving.
I have played all of the new Pokemon games that came out after X and Y, And they are so fun to play nuslog with because it's so much easier to get a pokemon's level up so it is viable, and Because they have so many pokemon's to use, just makes it so fun to nuzlocke.
What I am trying to say is the game is so Slow, that if you want to level up new pokemon's for nuzlocke, You're gonna be dying of boredom, and not even the normal type Pokemon that gives an absurd amount of XP can help.
So here are my two reasons for the low score, there are too few Pokemons and the game is way too slow. But I also get why people like it, because it has a unique charm. So played for yourself and see if that's enough for you.