Whenever I play a video game, I always get immersed in the experience. No matter how awful that said game may be or how poorly optimized it may be, I always get sucked into the visual world within that said game. For example, a 2005 action shooter called The Getaway: Black Monday for the PlayStation 2 was very poor in the technical department. It had tons of glitches and game breaking bugs. But I didn't despise it, in fact I love the game. It brings back so many nostalgic memories of when I was a kid and that's probably why I replay it from time to time.
But if there's one thing that does take me out from an immersive game-play world, it would be its ending. The Elder Scrolls V: Skyrim took me at least three months to beat the game (including all the guild quest-lines) but when I finally finished, the main story that is, I was disappointed. Before the ending of Skyrim, I was sucked into the fictional universe of Skyrim. So much so, that I never wanted it to end. Unfortunately it ended on such a bad note, that I can't bring myself to replay through the experience again.
Another example of such a poor video game ending is Dragon Age II. While the original Dragon Age had a fantastic approach to its ending, the sequel delivers on a whim. The amount of plot-holes and the lack of a satisfying closure (even if it was a cliffhanger) really does make the experience of Dragon Age 2 seem meaningless. There's two DLC's to Dragon Age 2 that helps continue that experience but they're rendered useless because of the poor plot-line that they follow. They're not as great as Dragon Age Origins DLC packs.
What my point is, is that most video games (both present and past) have such horrible endings that the experience in playing those games are rendered meaningless. I can pick out ten more examples of horrible game endings and detail them, but I won't do that. Instead, I'll simply list them in a proper numbered list. It's more convenient this way.
10. Splinter Cell: Double Agent
9. Splinter Cell: Conviction
8. Splinter Cell: Chaos Theory
7. Assassin's Creed (the first one)
6. Call of Duty (all games end on such an abrupt notice)
5. Star Wars Knights of the Old Republic (the first one)
3. Deus Ex: Human Revolution
2. Halo Reach
1. Mass Effect 3
There are more out there, but these are the top ten that I can name off the top of my head. Most of them are subjective to personal preference, but my ideal game ending would be one that takes all of your choices into considering and puts them to work. Every choice you make throughout a game should have a consequence at the end. For example, if you kill character A, his death should be connected in some meaningful way at the ending of a said game.
This is an RPG route, and is suitable to games that take a non-liner path progression. For games that are liner, good video game writing is all that's required to make their endings more enjoyable. The Metal Gear Solid series are a perfect example of such perfect game endings. Everything that has happened in the plot is taken into consideration at the end. After the climax is finished, every plot-hole is cleared up by most characters in a form of a codex call or a cut-scene. Afterwords, a small epilogue plays out and the screen fades to credit sequence.
Not every game has to go this approach. Depending on the genre of said game, it can be very tricky and expensive to make a perfect ending. But the problem is that so many games end on cliff-hangers and rely on either DLC packs or sequels to continue where that said game left off. This is a very cheap move on the developers part and is something consumers should be intolerable towards. Before being able to make the perfect video game ending, we have to first re-organize and re-evaluate what the term "DLC" really means. Because so far, in the industry, only Bethesda knows the full definition of DLC and knows where to apply it to in a game.
Lets follow their example. Hopefully, in about ten years from now, video game endings should be a problem of the past.