It's funny to read people saying they'd have probably found Star Trek boring as a young child because it was so serious, or whatever. I've been a fan since I was 4 (or younger, this is as far back as my memory goes) and I never found the original series anything less than fun and exciting. And I still have great love for all of the Irwin Allen shows.
No matter my opinion and even after all these years I still think the Jupiter II is very cool. It seems such a pity they designed a cool ship and then after the pilot (worked into the first few episodes) we never saw it fly again until the third season, which by then the show was in colour and so ridiculous it was practically unwatchable.
Actually, it took off in the second season premiere, stayed up for a few episodes before crashing down on a planet and meeting Wally Cox and his Chicken Monster.