It was a great series, from start to finish. There were some clunker episodes but not many. I wouldn't have expected such an ending, considering the start, but it was really enjoyable. I also think the ending doesn't denigrate the entire series. The characters still remember everything and were changed by the events they experienced in another reality.
My favorite part of the final block of episodes was in The Horrible Herd
: Those things are part fish, remember, they can swim!
: Whoa, what have we done?
: You mean, like, other than release unnatural super-predators into the ecosystem?
: It's best just to walk away from this one, kids. Just walk away...
That's what would have scared me as a kid, even as an adult, it's quite unsettling.