Personally I don't really see a problem with it. the wider the number of Pokemon gets, the more possible it becomes to tailor special teams as they release more Pokemon for the under represented types.
when it comes to the way Pokemon look... each version has had several misses. 3rd generations luvdisc got on my nerves for truly being bland, but then the unknown are just entirely pointless overall. some good, and some crud each generation.
Sometimes though the newer versions seem worth a look to me. I'm picking up platinum because among other things, they finally divided up the mechanics behind each element, and gave physical and mental attacks for all 17 types. this means Pokemon who couldn't use their own element well (nearly ALL dark and ghost Pokemon in 3rd gen due to stat dispersion, or even just physical types with originally special elements) get a second chance to shine a bit.
sure, they may be the same stamping out overall, but they do add or alter the mechanics a bit, or add something new overall like the 3rd and 4th generation Pokemon contests, so there are more things to do. personally my issue is your always locked into the gym battle thing. maybe I want to travel the whole revealed world to raise my snorlax to win cute competitions in every corner of the known Pokemon world. In my case, sticking a medal on my "little" (as little as roughly 1000 pounds) snorky is a lot more fun then another gym brawl.
As for each new one dropping so many Pokemon, I can only assume that each area is relatively in the dark about each other unless you actually go, which doesn't make much sense. maybe you won't hear the story of every region, but they all seem relatively self-contained. that could have something to do with it, but each region not being aware of the basic other one is kinda foolish, but they gotta ship sequels out somehow. still more diverse then other franchises, id say.
