I actually agree with this. It's part of the reason I find it hard to get into anything past Gold/Silver in terms of Pokemon. I love the games, I just don't give a **** about the Pokemon. To this day, about 90% of my favorites are Gen 1.
The first generation had creativity and intelligent design. With each generation, it seemed more focused on animal puns than interesting and original Pokemon.
I sort of agree with you, the 4th had a few good ones and i just didnt like the 5th, BUT the 2nd gen was better because it had more memorable pokemon and the third is Actually pretty good too, in my opinion its 2nd then 1st then 3rd then 4th then 5th