This has been addressed over and over again in many topics that often get locked for being repeat topics.
Each region is different to the last, their beliefs are different, the animals found their are different, the myths and legends of that region are different.
Each generation brings something new.
They aren't mechanic at all. They have mechanical parts or look metallic in origin but it is not always the case.
Besides, in a world where anything from a rock to a metal could be a Pokemon, does it really matter?
This trend has stretched back all the way to Generation I.
People are only starting to complain now because they're finally seeing the similarities.
And in my opinion, a true fan should stick by his/her franchise no matter what and that is what Pokecommunity continues to do to this day.
Fans who give up because they don't like a few designs in a new generation need to get over themselves and stop calling themselves fans, because they're not showing much loyalty to their franchise, are they?
You have to remember the core factor in Pokemon games, is in that they are made to appeal to the newer generation and the older generation(to some extent) but mostly to those of the newer generation.
Imagination is far and wide and they clearly have not run out of designs.
All this hub-bub about "running out of animals to use" is, to excuse my incorrect contextual usage of the word, utter bull because they have barely touched a fraction that is the animal kingdom. Barely touched a fraction of what is the legends and myths of different regions of the real world yet alone the Pokemon world.
I for one standby the fact that I will always support Pokemon no matter what it becomes because that is what a true fan does.
It's not going to stay behind and cater to your nostalgic needs in Generations 1 and 2 forever.
You are given the ultimatum to either stick with the programme and discover NEW types of monsters and legends in NEW areas with entirely NEW things.
Pidgey was a Pidgeon, Hoothoot was an owl, Tailow was a swallow and Starly was a starling.
All basic bird tyupe Pokemon but all originate from different types of birds.
Golduck originates from the Japanese Kappa myth.
Likewise, Suicune is a spirit of water.
Different things, different regions.
Stick by it or go the opposite way.
There is no use in complaining. If you don't like it, it's easier to just go away from it because it's not going to change back just because a few "fans" aren't willing to accept a Blaziken over a Charizard and so on...
Fans giving up on their franchises over a ridiculous reason such as it not being the same as it used to be is, to be honest, as said, RIDICULOUS!
It's called evolution, and no, that's not an intended unfunny pun, it's fact.
If the franchise remained the same as it did back in generation 1, it wouldn't have as many fans as it does now and we might not even have Pokecommunity.
Also, to further prove my point.
Pre-orders for B/W opened July 31st, 2010.
It hasn't even been a whole month yet and already there has been exactly 1.08 MILLION pre-orders down for the games and is expected to rise to 1.5 million pre-orders before the games are released in japan in exactly 23 days.
This is a record break for any pre-ordered Pokemon game ever made, even more so than generation 1, generation 2, 3 or even 4.
Black and White is the step forward.
Sorry about the long rant but I like to get my point across nice and clean with everything picked at and explained to the fullest so that issues like this don't need to be rose again.
Just deal with what Pokemon has given us and stop complaining about designs or meaningless aesthetics. ENJOY and be glad they're giving you games to play at all.