Which version counts?

The first time I read The Long Goodbye by Raymond Chandler, I was blown away.
It was my second Chandler novel after Farewell, My Lovely, and I was blown away once again by Chandler’s prose style, and by Philip Marlowe’s slow but dogged determination to get the truth about a dead friend resolved, even when though the friend is dead (allegedly suicide) and can’t care, and his equal willingness to help the living (“I’m a romantic … I hear voices crying in the night and I go out to see what’s the matter. You don’t make a dime that way.”).
Rereading it some years later, I was surprised how little it works. Knowing how the book ends, most of the story seemed draggy. But that didn’t entirely surprise me; a lot of books and films that I loved the first time don’t measure up the second time through; it takes a third viewing to recapture the appeal.
Not this time though. I read Long Goodbye once again and it really does drag. Without the mystery of his friend’s death to solve (since from my point of view, it’s solved), it’s mostly a long, meandering story about Marlowe helping a drunk friend avoid a possible murder rap, then trying to keep a drunk writer from killing himself, even knowing the odds are against success (I can’t help wondering if this doesn’t reflect Chandler’s own issues with booze—though knowing the answer wouldn’t make me like the book any better).
And no, this isn’t true of all Chandler’s books: Farewell My Lovely reads just as well the second time through. So it’s not rereading itself that’s the issue, it’s rereading this particular book.
So my question is, how do I rate the book? Based on my first reading? Based on rereading? In-between (“Great first read, doesn’t reread well.”)? It’s odd to think that I can’t just say “good” or “bad” about it and let that stand.
But I can’t.