Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Sincere and Unambiguous
Sure, ironic and ambiguous stuff happens in The Romance of Tristan. But we, the readers, are never left in any doubt about where our sympathies should lie, nor about how to interpret the things that happen in the story. When Tristan leaps from his bed to Yseut's, causing his wound to open, dripping blood on the floor, the narrator interjects a cry of 'What bad luck!' just to be sure we know to lament the outcome for our lovers (3.64).
The barons, we are told, have "acted very badly to the king in making him angry with Tristan": never is there any suggestion that the barons might have done the king a favor by convincing him to get rid of the guy who was sleeping with his wife.
The message is clear: Tristan and love = good, evil barons who thwart him and it = bad. Of course, just because the tone of the story seems to resolve thorny moral conundrums without a second thought doesn't mean that we can't question whether anyone or anything in The Romance of Tristan is really as uncomplicated as it seems.