I'd quite like a more in-depth SimEarth, a game where you can just sit back and watch things develop or watch how your interference in things plays out.
There would be a speed guage somewhere on screen, so one could progress (or regress) the time from up to billions of years per second down to single years per second. If one were to reverse the time, the future timeline would be erased leaving you at the point at which you stopped the reversal.
The game would begin at the creation of the planet from other large space rocks and it would end at the unlikely event of the total destruction of the planet either through sentient beings living on the planet or an external source.
Opportunities to change the atmosphere would be vast and unlimited and if any lifeforms appear, they'd evolve or die out according to the hardships in which they face. There would be no "Earth" species available for placing à la the original game because each species would be entirely procedurally generated according to the environment. There could be a tab to view the current life on the planet separated into simple groups such as "plant", "animal", "bacteria" etc. then split into further groups such as "algae", "fish", "positive cocci" etc., one could then click on one of the procedurally generated named for one of these living creatures (and rename it if so wished) and view a description of it with its length depending on how complex the organism is, so an "animal" would almost inevitably have more lines of text than a "bacteria".
In the event of intelligent life appearing, one could now click on a "sociological" tab, which (depending on how advanced this life is) would show the linguistic and cultural histories of the intelligent life perhaps an interfering player might be able to introduce new ideas to members of the populice with broad names such as "violence" or "egalitarianism", these could have broad affects depending upon the climate in which these ideas are introduced and the type of species they are introduced to. So for example, an intelligent species with scarce resources when introduced to violence might interpret that idea as being one of internal violence rather than external (each species would do their best to survive in any given situation and according to what they are able to do) in order to retain what little they had, perhaps they would become quite nihilistic, though I don't know how such a thing could be visually recorded.
I don't know if the player should have the ability to alter the shape of the planet manually or whether it should entirely be done through the introduction or addition of elements and chemicals and things.
Hopefully, this game would be just as interesting to a botanist as it would be to a geologist, physicist, sociologist, economist, chemist, zoologist...
I can't think this game will ever exist, but it is a nice thought.
Sorry for rambling a little!