Above all, any idea must hold to the "There Is No Tomorrow" idea.  The player has 24
  hours of gameplay.

Base defense idea:
  This military base has been strategically designed so that it can be held by a
    single person.  Which is good, because you're the only person unable to avoid
    being "volunteer"ed.  You are here to guard the escape of all other personnel
    until tomorrow, when the station will self-destruct to keep it out of the hands
    of the enemy.
  While the escape is still going on, friendlies will be around to provide various
    things.  Friendlies will sell food, updgrades, refills (instant refills, and
    refills that can be saved for later), and random junk the player can resell to
    other friendlies.  Some friendlies will sell blackmarket items like escape pod
    parts, and pieces of stolen alien weapons.  If you talk to the guy conducting the
    escape before he leaves, he will show you where an escape pod "will" be left for
    you to use.
  During the escape, the aliens will come in waves offloaded from ships through
    docking hatches at various distances from the escape hatches.
  Number of friendlies will gradually decrease, until all are gone after 12 hours.
  After the escape is finished, aliens will come in through all docking hatches.
  No more friendlies will be around to provide refills or updgrades, but there will
    still be some forgotten caches of them.  Also, the player may buy refills and
    save them for later, possibly stashing them in some out-of-the-way corner.
    Aliens will use or destroy any unguarded stash they find.  Some aliens will drop
    guns and/or ammo when killed, but their medkits are usually not compatible with
    your wounds.  Some of their food is barely digestible, and some of them can be
    cooked and eaten safely.
  After that, your sole purpose is to kill as many aliens as possible, and goad the
    aliens into flinging more resources at the station.  The higher the number of
    aliens killed, the higher the overall score.
  At the last minute, (or before), you may attempt to escape.
  If you do not attempt to escape, you die in the explosion.  This has no direct bad
    effects on your score, though it may be possible to kill more aliens if you
    choose an escape method.
  If you reserved an escape pod, you will find that is has been used by some
    unscrupulous escapee.  This can be prevented by staying by the escape pod and
    guarding it.  Occasionally, a friendly will run by on the way to a different pod.
    At some point, a large crowd of friendlies runs in and gets into pods and
    leaves.  After the crowd clears, your pod is gone.  If you massacre the crowd and
    keep them all away from your pod (yes, they fight back), it gets left for you.
    If aliens find the pod, they will treat it as a stash, either using or destroying
    it.
  If you bought the right things (including instruction books) and have enough time,
    you may build an escape pod from the pieces purchased on the black market (or
    pilfered from other pods).
  If you launch successfully, several things can occur, depending on time left.
    1.  You left too soon.  The aliens avert the self-destruct and use the station to
      destroy the escape fleet, you included.
    2.  The Feds have given up on you, so there isn't a ship waiting to pick you up.
    3.  An alien ship saw your pod.  It decides to pick you up.  Your pod is boarded
      by a small party of aliens.  If you defeat them, you may board the ship, see
      alien ship section for details, but ignore the bit about the flex-tube.
    4.  You left too late.  You are caught in the explosion of the station.
  The alien ships can be boarded at any time (even during the escape) through the
    flex-tubes connecting them to the docking hatches.  However, the aliens will blow
    the flex-tube if you try, so you have to be faster than their reflexes.  If you
    make it through the tube, you end in an airlock that is unfortunately, controlled
    from the control room of the ship.  If you cannot blast through the door, you get
    ejected into space.  If you make it through the door, the ship undocks to carry
    you away from the station and leave it open to the other ships.  The other alien
    ships *really* start piling on and offloading troops when this happens.  You are
    under continuous attack while you are on the ship, aliens come in through the
    doors of corridors constantly, though there are only so many aliens on the ship
    (but you only have so much ammo...).  A very heavy guard is maintained around the
    Control Room for the ship.  If you successfully take the Control Room, the ship
    is yours to control.
    It has various capabilities.
      You may fly it anywhere, and you may attack other alien ships with it.  If you
        attack other alien ships with it, they will attack you, otherwise, you will
        be left alone by them, unless you attempt to communicate.
      The ship has hyperspace capabilities, so you can fly it to any nearby system.
        If you fly it to a human system, the local fleet thinks you are an alien and
        destroys you.
      You may load an escape pod onto the ship to use later.
        You may launch the pod at any time, see the successful pod launch section
          above, with the additional choice of using the pod to return to the
          station.  Also, the direction of the launch may be chosen to avoid or
          intercept other ships, affecting the chances of being picked up.
        If you take the ship to a human system, then leave in the pod near the edge
          of the system, before being seen, you can be rescued and survive to get a
          medal, though the game ends.  If you attempt this before the escape
          finishes, you get reprimanded and sent back to the station, this time with
          no pod.  If you massecred the crowd to guard your pod, and anybody survived
          to tell about it, the victims' families declare a vendetta against you and
          you must flee/fight your way to a different planet.
      The ship may dock with the station, another ship, or an escape pod.  If you
          dock with another ship or a part of the station controlled by aliens, you
          will be met by a medium-sized boarding party of aliens upon docking.  If
          you dock with an escape pod, it might contain friendlies, or aliens,
          depending on its launch site.
    Any number of alien ships may be commandeered this way, though the aliens will
      retake any unguarded ship that is docked with the station or another alien ship.
  Some side notes:
    While food isn't abosolutely necessary, top speed, vision, and endurance degrade
      if you don't eat enough.  This degradation will be controlled by a sorta "blood
      sugar level" system.  Different foods will affect it differently, some
      negatively.
        Top speed stays the same until bsl falls below a certain point,
          then it declines at a constant rate.
        Vision doesn't degrade until bsl gets very low, and has a minimum (the player
          has to still be able to play).
        Endurance actually means how much damage you take from a given injury.  It
          slowly but steadily gets worse as bsl decreases, until you take double or
          triple damage.
      Some special foods restore health or give boosts to speed and/or endurance
        beyond the normal.
    You have a limited carrying capacity, thus, some things must be stashed in safe
      places.  Guard your stashes well.