I was on the Kop that night. Rest of the ground was not far off empty but the atmosphere that night was up there with any of our recent CL nights and EL nights including Chelsea and Dortmund
Probably not quite Chelsea in 05 but I'd say it was better than Dortmund.
We had a lot more raw aggression back then. When people talk about atmosphere they sometimes only consider the singing. Things like the cheering of every 50 50 ball, whistling and the drone when they had the ball, getting on the ref's back every opportunity, the general roar every time we went forward with the ball. Not forgetting the simple Liverpool chant.
All that kind of thing is missing now, even on Euro nights. Sorely missed aspects of the atmosphere when people are talking about how it was.
Singing was only one part of the great atmosphere, not the only part though.
That's what we really need back. It's OK to only sing when we're winning, as long as you're making a general din when we're not.