POLITICAL ASSUMPTIONS
Civ1 is the most left-leaning of all games. Later versions used all sorts of solutions that has pushed this game more into the right. Introduction of fundamentalism and nullification of civilopedia entry about anarchy as a valid political alternative for governments has pushed Civ2 to the right on philosophical spectrum. Global warming and pollution are getting less and less important in later games, making a hidden statement that industrial civilization can be in balance with global ecosystem. Social unrests are also getting less painful. I understand that designers were aiming at higher playability but it's interesting that making a fun and less annoying game forced development team to introduce (or reduce) concepts that makes this title more right-leaning.
I love Civ1 because it was one and only game that acknowledged anarchism as a philosophy, not state of chaos. Even if it's impossible to play such Civ and I believe that it's rightly so. Utopian philosophies should be saved for post-2000AD period which isn't covered by Civ.
POLLUTION & ECOSYSTEM
I love it also because of the pollution but I have one problem with it. Well... Civ1 is too optimistic when it comes to global pollution. Mass transit and recycling as cures for global consequences of massive industrialization? With AI civs managing their pollutions very well it's almost impossible to induce global warming without nuclear war or deliberate actions. Btw, sometimes it can be beneficial to destroy the eco system just remember that rivers and hills are immune to global warming. Besides, deserts that turn into swamp can be turned to grasslands.
Trust me, Earth map flooded with swamps is so cool to play on!
What I don't like in all Civ games is that climate lacks dynamics. Except for effects of pollutions or fallout areas, the climate is stable and it doesn't correspond to the data that we posses today. Sahara was a lush grasslands somewhere around 3000 BC but Civ games don't reflect that. There are far fewer forests on Earth maps then there were in reality, prior to human deforestation.
BUGS!
You heard me! Instead of bugs that crashed the game, Civ has plenty of really cool, playable bugs. I haven't noticed those on random maps but on EARTH map once in few games you can encounter really cool things. Some examples:
* Once in a time I get a city that I cannot conquer through the use of force. I can enter and even fortify a unit inside but somehow I cannot attack its defenses.
* Ultra-productive terrains over Canada. New type of tiles appear, making all resources off-scale even when working one tile.
* East of Australia I sometimes get a polluted sea square. You can clean it with settler on a ship but it's so unique and cool that I rarely do that.
* Once I got only some advances from the higher-end of technological tree, giving me access to end-game period units in gunpowder era. Look, I was really loosing the game at that point but getting almost invincible units turned this game intro really interesting one.