Guess what guys! It looks like Kelly Bailey, the main composer of HL soundtrack, is no longer working at Valve. I’m really concerned about the future of HL series now. I just can’t imagine any HL game without Bailey’s music.
check this forum for more info: https://forums.steampowered.com/forums/showthread.php?t=1781962
EDIT:
For anyone interested in Bailey’s departure from Valve, check out this interview with Mike Morasky: https://www.podcast17.com/interviews/audio/mike-morasky/
The discussion about Kelly Bailey starts at 00:26:10.