#1: Kyle XY was getting really friggin' awesome, and then it ended on a cliffhanger.
#2: Tremors: The Series had the potential to be one of those little shows that weren't mainstream but had a loyal following. It ran for only 13 episodes and the last one was anti-climactic.
#3: The Flash (1991 live action series). This show had TONS of potential to be one of the greats. However, it ran for only one season because the network gave it a poor slot in between much more popular shows at the time, and went so far as to frequently switch the program schedules.
#4: Spiderman: Unlimited. People were split down the middle on this show for two reasons: One, the spiderman suit was changed to a more technologically based outfit (with a cape made of spiderwebs), and the story took place on an alternate earth that Peter had become trapped on (it was like the Batman Beyond version of Spiderman, now that I think about it). It had potential, but sadly ended on a cliffhanger.
Hellsing: It ended on such a cliffhanger that I don't know what
Sir Integra decided while her and Alucard were locked away after what happened
Adventures of Brisco County Jr. & Firefly & seaQuest DSV/2038: All three shows I love that were CUT SHORT and never renewed or cut mid-season when things were getting really good
Fullmetal Alchemist: Does it need saying?
Al and Ed
crying
Doctor Who: Most episodes themselves almost always have a heart-shattering ending!
Gurren Lagann: Poor Simon!!!! Poor Yoko!!!! I didn't want Kamina & Kittan to die! I hope Yoko found someone who made her happy. Kamina, the first guy she loved, was stabbed & bled to death. Seven years later, her second love, Kittan, died in an explosion. Then 20 years later, she's a middle aged school principal. Did she ever find someone else? I really shipped Yoko & Kamina! I wanted them to get together! I'm happy they Simon & Nia got married. But then Nia died! Wtf! And then 20 yrs later, Simon is a lonely man, wandering the world with his pet Boota. Also, he had left Dai Gurren 20 yrs ago and left all his duties to his friends. I hated the ending.
Samurai X: Trust and Betrayal OVA is the first thing that comes to mind. I'm sure there have been others, but I don't remember them. My memory is terrible.
The ending of Vision of Escaflowne... it was such a bittersweet ending, in my opinion it would have been better if it showed the wedding of Van and Hitomi, and the latter's family and friends were sitting beside Merle during the ceremony.
Being Human's finale was really sad. The characters all ended up in better place, but it's still sad that we weren't able to spend more time with them.
The Secret Diary of a Call Girl shattered my heart because Season 4 does not exist. It does not exist.
If you've watched it, you'll understand my reaction.
I'm still not over Young Justice.
I will never be over Young Justice.