The designs are a lot more complex than usual. Some of them aren't bad, but they don't mesh very well with a lot of the older ones. :/
Also, on the topic of how the monsters are made: So, there's a team of people that is in charge of monster design.
http://bulbapedia.bulbagarden.net/wiki/Staff_of_Pokémon_Red_and_Green
They're listed under "Pokemon Design." They come up with the ideas. They decide which ones are the best, and refine them. Then, Sugimori-san draws those designs. In the first gen, it was a group of four (Sugimori-san being one of them), and Tajiri-san's role in creating the monsters was basically to approve them, and suggest changes after the basic ideas were being designed. He's the only one under "Director" and "Game Design" which means that he was in charge of pulling everything together and the overall experience of playing the game.
Nowadays... well, the truth is that in R/S, Masuda-san took over. Ever since R/S/E, Tajiri-san has
not been working on the games at all. He's listed as "Executive Director" in most games. What does this mean? "Ex. Director" is a fancy way of saying "this is the original creator, he approved this game but was not an active part of development." Occasionally he's listed as an "Ex. Producer" which, from what I can gather, means he funded it but was still not an active member in developing it. Finally, in Pokemon Rumble (surprisingly enough), only Sugimori-san and Masuda-san are listed in the credits as "advisors" for the spin-off game. Tajiri-san is not listed
at all.
So, he's not really putting his mind into the monsters anymore. However, there is another part of why the monsters look different. The "Pokemon Design" of D/P/Pt was held by thirteen people. Ten of these people did not work on R/G's mons; Morimoto-san (he's the guy who put Mew into the game) also stopped doing monster design during D/P/Pt. What does this mean? The people coming up with the ideas are, mostly, different each Gen. R/S hired a ton of people, and that's why Gen III's style was so different. B/W has also hired more people (GF was recruiting graphic designers - remember? They're usually the ones in charge of monster design too) so the designs will be very different.
TLDR; version: The main reason why the B/W mons look weird is because the design team has some new people on it. Also, Tajiri-san hasn't worked on the games for a looooong time (G/S). Thus, the reason why Gen III and Gen IV looked so different from Gen I and Gen II. And now Gen V is going to be very different as well.