Lonesome Dove is probably the most faithful adaptation of a novel but it took a multipart miniseries and a near perfect cast to do it right.
I respectfully but passionately disagree. While the cast is mostly perfect (Blue Duck was egregiously badly cast), the adaptation bungles virtually all the revisionism and subtext of the novel and spins it into the grand Western myth that it sought to deconstruct. It's like taking Unforgiven and turning it into Stagecoach. A complete violation of the spirit and tone.
Even at its length, it still had to truncate and simplify the various storylines, utterly butchering some to cliffnotes (July was possibly my favorite character in the novel and he's a blip in this film).
A great example of the limitations of adapting an epic novel to film. It gets most of the plot right but little of the essence, which I think is ultimately far more important.
This is why something like Let The Right One In is such a great adaptation (script from the original author, no less). It adopts an iceberg approach, catching glimpses of the novel's larger world (which would take a miniseries to fully render) but perfectly capturing the essence and important beats. It wouldn't be any greater with 6+ more hours just to go into Hakan's pedophilia, Eli's origin, or their detective neighbor's relationship with his son. It would probably feel a great deal lesser because fidelity would override what's best for it in it's new form.
So to answer the OP, there are many books I would love to see get faithful adaptations. But faithful to the essence and not adherent to every plot point or layer of character. I'd love to see McCarthy's The Crossing (which makes the think of All The Pretty Horses, which similarly got the plot points right and the feel completely wrong).