Hi LaMarche,

except for the last question about Modding I can give you insight to the first two questions:

Games that remember: The Gothic franchise
Games with consequences about what you do: The Gothic franchise; also Knights of the Old Republic, which has plenty of "parallels" to the Mass Effect series - in fact I learned and understood playing Mass Effect because I "trained" the same basic oncepts in Knights of the Old Republic.

If you enjoy sandboxing combined with some incredible economic flavor: go get yourself the X-games from egosoft - www.egosoft.com. These games put some spells on me. And the modder-scene is impressive and huge.

Best wishes!
Liam