Yeah, I the few people I know who went did so during the spring and liked all the animals and everything. They suggested it but its a little far for us for just a casual outing lol
We went last summer. Great place, I'll go back again this year now that DS is REALLY into animals. I wouldn't want to go there when it's been wet, as it seems like it'd be pretty muddy in many places. So I'd wait until it's nice and dry. Also, there's access to Issaquah creek, which is nice when it's hot out.