One games gameplay meets another's universe

I'm trying to mix things up so not a list or a review just some cool ideas. I think every one has had a what if these crossed over idea whether it be Movies, Television shows, or in my case video games. I've thought up 5 what if  crossover scenarios that I believe could be completely plausible. Of course we'll likely never see any of them actually made because things aren't that simple. Still without further ado my five crossover ideas.

Halo / Dead Space

Now in Halo your generally filling the shoes of super solider Master Chief, who can stop entire armies essentially single handedly. In Halo ODST we were brought down into the shoes of an ODST who are Halo's equivalent to Seal team 6. We've always seen the UNSC grunts we know they're there but have you ever thought about how awful the entire series of conflict must be to the regular soldiers? They don't get advanced armors, weapons, or gear like the Spartans or ODST. They are also vulnerable to Halos Parasite race the Flood. The flood are scary enough behind Armor imagine if they had the upper hand? Like the necromorphs do in Dead space. Imagine walking through a building and if even a spore flood gets the drop on you your dead?

Here to set the mood

So that's the premise for my first idea. The Game would take place between Halo 2 and 3. Your a marine sent to assist a Colony against an attack presumably the Covenant. When your ship arrives the Covenant are quickly retreating, which is highly unusual. Chasing them isn't your priority though, its checking the colony for any survivors. Your team is dispatched to the surface where you quickly find out why the covenant were retreating. After confirming flood presence your team is quickly picked off. Your Evac isn't possible so you are left to fight their way through the dead colony to a new evac zone.

The second course of the game or sequel would have your ship emerge from slipspace only to find itself on a collision course with High Charity the covenants former home, now fully taken over by the Flood and hurtling through space towards earth. Your only option is to try and find an escape route off the ship before you die.

Fallout / LA Noire

Fallout is an open world game where you traverse the remnants of a post apocalyptic alternate reality America. In Fallout's world technology greatly surpassed our own but culture was stuck at the 1920-1930's level. The only time we get to see or here about Pre-nuked america in Fallout is through occasional flashbacks or in written/recorded logs scattered though out the game. Where you can find out some details like how the tensions were rising before the attack and some minor details like recent technology. Of course we get to see many things left over from before like car designs and robots but we never got to see things at their prime. we've never seen a living version of Fallout's world.

That is until we get an open world L.A. Noire style game set in D.C. before it was known as the capitol wasteland. Cars and people still moving along, going about there days not knowing their end was approaching. You'd play a federal agent tracking possible chinese militants hoping to stop whatever they are planning, of course like Halo Reach, from the beginning you know the end. But you'd get to explore the entirety of the Fallout 3 map before it was reduced to ruins. You'd get to hear the anti-communist propaganda, the liberation of Anchorage, the rise of Vault-tec, Nuka cola, and other corporations before the bombs fell and stopped time in the fallout universe.

Fable / Dark souls

So if your like me you though Fable 3 was awful and did way too much to hold your hand. You felt the game was lacking any real challenge. Even Fable 2 was incredibly easy but at least that had a decent story and world. Now what happens when you match a colorful and often humorous world with a gruelingly hard combat system and much more in depth equipment system?

so maybe fable wasn't always sunshine and rainbows

I'd imagine something pretty awesome. Both games would finish each other getting rid of Fables ridiculously low difficulty level and Dark soul's ridiculously drab setting. The game would predate Fable one at the founding of the Hero's guild. Albion is in chaos there is hardly a place that could be considered safe with nothing to cut them back Albion's traditional enemies are much stronger and more vicious. Using an artifact that would later be destroyed and forgotten, The hero's must sacrifice something precious to obtain pseudo immortality. However if they are slain in battle they will return much weaker and their obtained exp will be lost. The goal of the game is to tame the land and establish the Hero's guild.

Mass Effect / Battlefield

This is the only one i'm writing about with multiplayer in the forefront of my idea. I was originally going to say Call of duty instead of Battlefield but I think Battlefield's class system would work out much better. Not to mention the vehicular combat could be interesting as we've only seen a few of Mass effect vehicles. The teams would be N7 Vs. Cerberus else of course players would be limited to humanoid size characters for balance reasons. The game would be in Mass Effects universe but using Battlefields engine to allow destructible environments.  The maps and weapons would be based around those from the Trilogy.
The Biotic/Tech powers would be the biggest difference maker to conventional gameplay though. Many might have to not make it for balance reasons. Imagine using Tech armor to gain a slight advantage in combat or closing the distance with a biotic charge?

Is this picture from Mass Effect or Battlefield?

I don't know about story mode though, I honestly don't see when this could fit in. Possibly between ME 2/3?
It could focus on a campaign to stop the Illusive man and Cerberus' plans. It could be interesting to see a more combat focus take on the Mass effect universe. even still its actually the most plausible idea on this list considering both series are EA.

Gears of war / Last of Us 

Speaking of plausible it needs to get thrown out the window for this idea. So through out Gears we play Marcus Fenix and Delta squad as they fight back the Locust invaders. Even though the Cog are already at the losing end of the battle when we're introduced they're still a trained army with years worth of combat intel. But what about those civilians and non Cog militia types called the Stranded we see here and there?
How have they managed to survive an enemy that's crippled their entire planets military/government? Whats it like for those who abruptly have to move through a hostile landscape?

How/why did people live on this planet before the locust came anyway? This had to be an issue...

That's where this game takes place. Your a stranded who's settlement gets overrun by the locust you have to make it to another settlement or die trying. of course this wouldn't be much Last of us unless you had a companion. You have to escort the Daughter of a friend who's last wish was for you to get her to safety. Without food, weapons, and shelter you must make it across Sera's harsh landscape. Along the way you'll have to avoid locust patrols, Kryll, and avoid dangerous weather like Razor hail.