I can't help but complain at people who talk like this. 1st gen had BARELY any originality. Most of it was just faces attached to objects or random anthropomorphized animals, some are ugly creatures based off human professions like body builders, mimes, and opera singers. Sure, there were still cool designs despite that, but 1st gen monsters weren't all that great.
5th gen I felt had more thought put into the designs. Sure, and ice cream cone does seem like a pretty random idea, but there are still plenty of cool ideas. You got a samurai sea lion, a massive centipede who looks completely boss, and an adorably plump ninja who devastates the field. I even admit to liking some of the unpopular designs like Garbodor, who I think looks cute in a silly sort of way.
Honestly, the more people I meet who complain about how much the later gen monsters are garbage, the less respect I have to first generation Pokemon.
As for no replay value, I just felt they could have included more things to do to break up the monotony of regular battling. Cause that Pokemon Musical just doesn't cut it.