Irwin Allen's writers seem to be obsessed with aliens taking over or trying to destroy Earth. The Time Tunnel in the end was reduced to this in the end. The only difference was they were travelling through time. Voyage to the Bottom of the Sea in the final two seasons was made up of a number of such episodes.

Two other things Irwin Allen shows had in common:
The pilot episode of each series was directed by Irwin Allen himself.
and
They all guest-starred Michael Ansara and Warren Stevens
Something three of the series had in common: all the cars were supplied by Chrysler.

both shows LIS and 'voyage' had great potential, but they were geared for the kids so it was great for a kid like me to watch , its only when you grow up , you realise how dumb they were.

You should watch more Time Tunnel episodes, it was a vastly superior show to Voyage or any other IA shows as far as continuity, concept canon, and just solidity to an idea. It was consistently somewhat plausible most of the time, unlike any of the other shows.

The Jonathan Harris Comedy Hour?
LOL! My kid sister used to refer to it as 'The Dr. Smith Show'!

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Season 1 of VTTBOTS contains roughly 70% episodes that are decent or good, with a couple of those being excellent. Season 2 of VTTBOTS contains about 10 episodes that are decent or good, my favorite of which is the first of the two 'Phantom' episodes, which featured the ghostly WWI German U-Boat captain.
The rest of VTTBOTS is mostly watchable for the FX, or because Capt. Crane and Kowalski are like old friends to us, or for goofy fun like playing the 'let's ID the source of this episode's stock footage' game. Some episodes are, however, unwatchable.
VTTBOTS is the pinnacle of IA's TV showscompared to IA's other shows, it's like The Sopranos.
Lost In Space has a number of decent to good episodes, mostly in the first half of Season 1, but also with a few decent episodes in S2 and S3 (notably the goofy but great 'Anti-Matter Man' episode). Most of LIS is unwatchable to an adult, largely due to the quasi-pedophiliac relationship between Dr. Smith and Will Robinson.
Only seen a couple eps of Time Tunnel. Mostly meh, but in general not as painful as LIS season 2 or season 3.
LOTG have only seen about 3 episodes. Awful stuff, probably the most pointless of all IA's shows, but the pretty girls were fun to watch. How the hell did LOTG get renewed for a second season, while all the other fantasy shows of the 1960's were dying off en masse in 1969 is one of the great mysteries of TV.
The film of VTTBOTS is classic IA, in that it is pointless, silly, and mostly unwatchable. I got through about 30 minutes of it. Just complete idiocy, especially the characters. Same is true of IA's version of Lost World, footage of which shows up in a couple VTTBOTS episodes.
The greatest part of IA's legacy is pure schlock, much of it unwatchable. There are, however, a few gems, like early VTTBOTS and LIS, and maybe the Poseidon Adventure, that are worth watching.

I don't know if any episode of Allen's shows would qualify as sublime, as 95% of them were barely mediocre at best (with a whole lot of them downright awful.) One notable exception was the
Lost in Space
episode where Michael J. Pollard played a teenager caught in a mirror dimension. That episode was in fact really quite good and hinted at how
Lost in Space
could have been much better if they had really tried. The first season of
Voyage
wasn't that bad, but somewhere during season two it seemed like they kind of gave up and stopped trying. Stories were all the same, they just changed the type of monster they faced each week (this week it's a giant underwater spider (???!!), next week it'll be a giant sentient sponge). One episode had the most ridiculous plot point ever: the Seaview was helping place nuclear bombs to build an underwater canal. Of what conceivable purpose was a canal on the ocean floor?
One other thing I noticed was that the best episode for
Voyage
and
Lost in Space
were when they were in B&W. Once they went to color the quality of the shows dropped dramatically. This is especially interesting since Voyage premiered a year earlier and was already in color during Lost in Space's first B&W season.
I'm ignoring
Time Tunnel
and
Land of the Giants
as both of these shows appeared to be little more than kiddie programs.