In Mass Effect 3, quite a few events depend on how decisions from Mass Effect 1 and 2 turned out. The game shows what decisions I made when I imported the save at the beginning, but once I am already playing, is there any way to see or determine what decisions I made in the previous games?
There is no way to determine what decisions you made in past games once you're actually playing the game, except by viewing the outcomes of those decisions.
If you converted the Heretic Geth in ME2, then you will face more resistance in the Geth related missions, but upon completion, if you have the geth on your side, they will be stronger.
There are just too many variables for them to list them all, and even the decisions they show you when importing your file are only a few important ones out of the many.