He was replying to a comment that stated that they didn't enjoy Half-Life but wished they had, and that Black Mesa let them do that. The reply is correct; Black Mesa and Half-Life are different games.
Half-Life is a good game, but it's also overrated because it was so novel for being narrative-driven at the time. It's still a Quake-like arcade shooter at its core, which is great but not new anymore, so people going back and playing the original expecting to be surprised may be disappointed.
People may be disappointed, people may feel like the commenters in this thread do, and people may appreciate both.
This is why it's ridiculous to ask someone else not to express their opinion on which is better.