Personally speaking, there are two ideas I'd really love to see:
Aliens: Colonial Marines done right. Yes, the game we received was a bit of a disaster, but the Colonial Marines are one of the more memorable aspects of the franchise. They have weaponry that can cut through xenos, but what seems to be forgotten more and more nowadays is that the aliens are truly deadly creatures, even if you do have a trusty pulse rifle in your hands. AvP:GE got it pretty right in this regard- a burst from your weapons would cut off limbs and blow them apart, but they were fast enough to make it hard for you and deadly enough that even just one up close could do some serious damage.
I think to get closer to the themes, they should look at games like the original three Rainbow 6 games and Space Hulk 2. These games are not without issue (especially Space Hulk 2), but it did give you the feel of both being part of a "badass" squad while still completely vulnerable. Your weapons would make short work of enemies but they too could make short work of you. When my team-mates started dropping, there would sometimes be an expression akin to what Gorman felt like when things started to go wrong in the atmosphere processor. Heck, one particular brutal encounter in the Space Hulk game had a genestealer manage to down one of my squad protecting one of our flanks because his gun jammed. This allowed the aliens to pour in through that gap and force my squad apart. More died as a consequence as I desperately tried to salvage the situation while fighting off genestealers myself. I had to try different tactics, make hard sacrifices and watch as nothing worked. More and more of my squad died, until finally, it was just me and the other only survivor cornered in a room making a final last stand before being overwhelmed. That was the sort of thing I hoped for with A:CM instead of the safer (but badly implemented) by the numbers game that we got.
The next would be somewhat of an open ended survival horror/action game where you play a member of a colony that comes into contact with the aliens. The focus would be on survival as the horror you face becomes bigger and bigger. At the start of the scenario, the aliens don't particularly make their presence felt- a few people go missing, there's some damage to things in the shafts etc- but as the game progresses they start to become this unstoppable force that you can't really combat. All you can do is try to survive and hope they don't take notice. Their presence divides the colony and makes food, weapons and safe havens harder and harder to find, to the point where other humans start to become suspicious, paranoid and very protective of what they have. NPCs in your group are all very expendable but react to events as they unfold. They'll question your decisions, support your choices, get angry at you or seek comfort from you depending on how you treat them and how they perceive things to be unfolding. Decisions are to be weighed heavily as everything is a risk.
I would doubt that we have the technical capabilities yet for this game, but I have played a few things which do capture the feeling of fragility and survival quite well.
