It's absolutely the most important skill if your a playing professionally. Still important if a semi-pro or recreation player. The only time it's not a skill or important is if you are a billionaire.
Bluffing works best in live poker against good players. Bad players can't be bluffed online or live as a general rule. The tells are fewer online as well. All in all online poker is good for practice or fattening your bankroll.
In my opinion it's a video game when played online.
Poker is a...