There is no album that is like Dark Side of the Moon. That is why it is so highly revered and thought of as one of the best if not the best album ever made, another good Pink Floyd song which has a similar feel is echoes.

http://www.youtube.com/watch?v=xmADpBu_ZCA

The half life series are very story focused games with a lot of characterisation so people are invested in the characters. The last game, Half life 2: episode 2, ended on a huge cliffhanger with several of the characters in very troubling situations so people want to know what happens next and they've had to wait 10 years.