Hmmm...I'll take a different route...
Instead of listing the five worst episodes....I will also go by category for each series.
1. TOS- anything where---- a certain--captain--speaks--in broken-----paced----sentences. That is----the ---most annoying----part.
2. TNG- Time Travel...period. About as easy as putting on a pair of socks.
3. Hard to say....I loved DS9.
4. Anything involving those overgrown Oompa Loompas known as the Kazon.
5. Enterprise--tough to say....need to see more, but like what I see so far.
Respectfully,
General Chang
Re: Hmmm...I'll take a different route...
Enterprise - Unexpected: Strange aliens flying in ships with trippy 60's decor, have cloaks, and apparently run on engine exhaust. Klingons getting holodecks 200 years before they mass-marketed. D-7 model being used for the Klingon battlecruiser. This episode also started the trend that every race has higher tech than the humans.
TOS - Spock's Brain: Not much to add that hasn't been said by hundreds of people throughout the years. There are probably a worse TOS episode out there but this just sticks in my mind.
DS9 - One Little Ship: I hate "Incredible Shrinking Cast Member" episodes that seem to slip into any sci-fi show. I was waiting for Rick Moranis to show up. Bad.
TNG - Rascals: Another of those "sci-fi schtick" episodes that creep into sci-fi series (you know, turned into babies, shrunk, mutated into lemurs, etc). Select members of the crew are turned into babies. This was compounded by the fact that the Enterprise, Galaxy-class starship and flagship of the fleet is captured by 2 aging Bird of Prey commanded by cowardly Ferengi. Ugh.
Voyager - Threshold: Paris does what thousands of Federation scientists have been unable to do and does it on a ship without reliable power or supplies. Then he turns into a lizard and mates with the captain. Probably the worst Trek episode ever, in my personal opinion.