I tend to let the real me (mood-of-the-day included) influence my decisions in games, however, the knowledge that i can alway reload or restart or something makes decisions in games SO MUCH EASIER... For instance, Hitman: Absolution, it's a great game but failed to grasp my attention and "perfectionism" the way the rest of the franchise used to. The whole "just get to the door unnoticed" and "you're being hunted" totally killed the Hitman mood for me to the point that sometimes I see myself just shooting my way to the end of the level (something I'd never do if in other Hitman games). However, if a game truly pleases me and is genuine in making me feel like I'm in control, like Fallout 3, then I let the real take control and take the decisions based on what I'd do if I was placed in a similar situation.
I don't play MMORPG OR FPS Online, the lack of a story and "interactivity" takes away any pleasure in gaming for me. As far as online goes I only do co-op online and only if it's integrated with the campaign in some way.