...just being curious

Over the years, I have seen several projects taken quite far before getting cancelled.

In the past few years, two amazing games from my workplace come to mind. The first was Wildlife: Forest Survival which was quite fun to play; within the studio we still have competitions on the game. It was nearly complete, but cancelled because of various budgetary concerns at the global level. The second was My Garden (there were so many other wonderful working titles that were not approved...) that was complete and ready for certification as a 3DS launch title, but right before launch the expected demograhpics of the 3DS changed, the estimates for number of 3DS sales plummeted, and marketers couldn't find a way to make the demographics of a zen garden fit nicely with the expected demographics of the 3DS, all of them combined for corporate to indefinitely suspend the project.

If you talk to industry veterans nearly all of them have stories to tell about incredibly fun games that are developed, some even finished and certified by first parties and ratings companies, only to be cancelled for various corporate reasons. Most people don't realize that marketing, distributing, and supporting a game have a combined cost of about 1/3 of the total cost. Both corporate politics and market research change during development. It can make sense politically or economically to abandon a game before the final 1/3 is spent.

Ouya perhaps?

Dungeon Keeper 3 ... ( EA killed it's final production after taking over Bullfrog Studios )

Half-Life 3 ( or Half-Life 2 Episode 3 ) ... Valve went silent after Episode 2

Portal 3 ... Valve went silent. Portal 3 was supposedly going to be a tie-in to Half-Life 2 EP 3

I'll add a couple of smaller old ones.

First, a very very old one, back in 2000!

http://www.gamespot.com/stars-supernova-genesis/images/

It was from a very small studio. This was intended to be a bigger sequel from a small but very good game they did before. However, at some point the budget was cut from above and it never saw the light.

Then, a more recent one:

http://wtactics.org/

It started in 2010 and looked great. An open source TCG/CCG with quality art and a small community. Time went by, but it failed to materialize and after 4 years without results I think it can now be considered dead.

They had a lot of top notch art, good ideas, many people, but in the end nothing came out of it.

I think it also makes a good lesson for open source projects.

Basically, the owner/leader/initiator thought: let's make the project driven by the community. If everyone helps, even a bit, something cool should come out of it. Well, nope, sorry, that's not how it works. In order to make a game, you don't need a crowd, you need a few dedicated individuals. On one hand, it was great for the sense of community, there is no doubt about that. On the other, all these little helping hands didn't bring the project very far.

The game rules were still going in several directions and implementations too, from plugins, to desktop, to web.

Everyone made tiny contributions in their own direction. In the end, there was barely something playable at all.

The "community driven" creation process failed miserably.

Actually, I was part of it too once. In a month or so, I made them a basic but working online prototype. I showed them, they were happy. Then I said "I can also foresee that it'll be a long journey to move from this small prototype to a full-fledged game. It's too much to carry all on my shoulders, but I know how it should be done and could lead the way. In other words, a couple of other programmers should jump in, or at least one partner". Well, the message went in the void, the response was kind of: "it's an open source democracy, let's see if someone comes by and seems interested to give a glance at the code". Other programmers continued doing their things, didn't bother. I knew I could not do it alone, I left. I still think that if they took it the other way round, they could show a decent game by now. Instead, three years have passed and they're not one inch further.

Duke Nukem: Forever. I don't follow the industry that much...

Ouya perhaps?

I have one, but me developing for it ran into problems:

I don't (personally) have a good display for it;

I plugged it into an older flat-panel monitor, but this didn't work out so well.

the bigger problem with Andoid in-general I suspect is this:

the development tools are, kind of, complete crap...

doesn't help that for the Ouya you basically have to get different parts of the SDK from different places (Ouya, NVIDIA, Google), and then later have something auto-update and the whole thing effectively falls apart.

yeah...

Kingdoms of Amalur: Reckoning. This one was released but the company fell immediately into a black hole of debt. Ken Rolston, lead designer of TES3 Morrowind and TES4 Oblivion supposedly retired, but then they got him working on this title.

Granted, there might have been never a sequel since it was sort of an introduction to a MMO but, if that one was successful, I could have seen a KoA 2.

Stargate Worlds. I was in the very early alpha before it was cancelled. It was so buggy that it was kind of destined to fail, but the premise of the game was amazing. They had a really novel combat system in place with cover.

Half-Life 3 ( or Half-Life 2 Episode 3 ) ... Valve went silent after Episode 2

Portal 3 ... Valve went silent. Portal 3 was supposedly going to be a tie-in to Half-Life 2 EP 3

They're working on L4D3 at the moment. No indication really of any other projects.

Stargate Worlds. I was in the very early alpha before it was cancelled. It was so buggy that it was kind of destined to fail, but the premise of the game was amazing. They had a really novel combat system in place with cover.

I was working on the Stargate FPS game that happened to get cancelled the day that Stargate Worlds was announced... Stargate has had a bad run in video-game land