OK, today's idea is one that sort of blends elements from GTA and the sort of collect-a-thons I'm always going on about. You play as an alien (which is a pretty popular topic for me, since the concept of aliens is something which is highly variable and has a lot of scope for imagination) who has visited Earth to research the place for an invasion. Sounds pretty Invader Zim so far, so I'll quantify what exactly our alien friend is doing here and how he goes about doing it.
He has various objectives on the planet, which take place on locations all over Earth. His first and foremost is the research itself, which can be done by surreptitiously stealing and "beaming up" various samples of fauna and flora, before moving onto things like Earthling technology and valuable minerals. The alien is also interested in the culture of the planet, though without making it too educational, it plans to take as many examples from one fandom as possible (say the alien is interested in Sci-Fi, so it steals toy robots until it has upgraded the ship to be powerful enough to steal the 60ft long plastic UFO sign from a themed diner). Ideally, it should try to do this under the cover of darkness to avoid arousing suspicion with all these mysterious thefts for as long as possible.
He can choose to be discrete about his extra-terrestrial activities, or go nuts firing on the populance while fulfilling his goals, generally having a harder time of it but will ultimately having more fun. You'll be disguised as a human, though the disguise will be pretty poor to start with, so you'll be hiding in shadows a lot for the first half of the game. It'll be more sophisticated as you upgrade that element of your reconnaissance, allowing you to get into more places by fooling the Earthlings guarding the building. You'll still have a hard time avoiding UFO nuts and the local law enforcement and like GTA, repeated exposure brings up a sort of "sightings" star system which when filled up brings FBI and Black Ops types snooping around following up all these reports of an extra-terrestrial visitor. These stars show up whenever you're spotted doing something odd, such as beaming an item back to your ship while someone's watching or fluffing a conversation with an Earthling (sometimes amusingly) by saying something very wrong.
Again, similar to GTA, the world you'll be visiting will be several cities large with a lot of space between areas. Your "Flight of the Navigator"-like ship can transport you between cities quickly enough (good if you've been spotted one to many times in one area) but you can still explore the planet itself if you tire of the cities full of people. Of course the planet will be down in scale somewhat compared to the cities (the available cities will probably be whatever scale GTA:SA was, around 1:50 I think, with the planet being closer to 1:1000). I plan to make the cities a lot more explorable than most of these types of game allow, by actually letting you enter practically all the buildings and taking whatever's inside (though with stealth if possible).
Gameplay will flow in sorties to the planet, beaming a certain amount of objects per day (in a certain amount of total volume per day, based on your ship's cargo hold) from all over the planet and storing or selling them through your intergalactic contacts through interested parties. You may accept missions where a gourmet restaurant wants so many special food items (such as cows or sodas, or maybe even humans) or a rich citizen wants artifacts a certain color (so you'd be hunting around for purple objects, in a sort of homage to Bart Vs The Space Mutants). Selling goods and acquiring various rare specimens increases your funding and reputation, which go towards ship upgrades and equipment to assist you "on the job". The following list has the sort of upgrades I'm thinking of at the moment:
Disguise: Upgradeable from your original model. Currently, your disguise is only vaguely human and you can be easily spotted by any human as not being "local" if you're too close or in bright light. With upgrades, it'll be easier to convince Earthlings you're one of them and eventually convince them you're someone important enough that they would let into their homes or banks. Eventually, you may even be able to turn yourself invisible and avoid the humans altogether. A side-quest to acquire a better "human suit" may involve abducting a certain amount of test subjects to use for a convincing disguise, making the game slightly macabre as you walk around with pieces of people sewed on you trying to blend in.
Zapper: A weapon that discharges a certain amount of power can have all sorts of uses, ranging from shorting-out security devices to briefly stunning humans. Upgrades would allow you to charge things like generators or battery-operated gizmos with a sharper degree of accuracy (whereas normally you may end up frying electronic equipment with the wrong voltage).
Cargo Hold: A ship upgrade, you can use this to increase the size of the objects you'll be transporting from Earth. You can configure it to expand your capacity for biological specimens also. Initially, you'll only be able to beam certain sized objects a very limited amount of times, so in the early stages you'll want to beam worthwhile stuff only. Keep in mind a unique sample will be worth a lot more than the second and third pieces of that sample, so even the first piece of trash beamed off the planet will be valuable to start with (though you could probably avoid beaming up any more like it).
Transporter Beam: Another ship upgrade, this will be handy for moving huge objects from the planet. To start with you'll have a severe size restriction as to the type of things you can transport, probably limiting you to things smaller than a soccerball. The beam will need to be upgraded in tandem with your cargo hold in order to hold the bigger items.
So instead of a just a regular "aliens take over the planet" game, many variations of which have already been made (from the perspective of the attacking aliens and the defending humans alike), the alien in this case is simply using the planet to get rich and achieve fame and power before taking the planet by force, using what it has learned to take us out. It'd be cool to sort of take on an Invader Zim sense of morbidness and the humor inherent in the major culture clash of a vicious imperial alien race and the otherwise backwoods inferior human race, but the chances are the game will need to veer away from that angle to avoid too many comparisons.
