*sigh* This is more of a ramble than a review, sorry.
tl;dr: Fantastic story, godawful versions.
Another post just reminded me of struggling through this last month when daughter had it as assigned reading.
Don't get me wrong, I love me some Tristan and Isolde. It's one of my favourite tales, it really is. But this translation.... daughter looked at me utterly blankly after a chapter and said she didn't understand any of it. I didn't make it that far, I got to about page 2 before throwing up my hands in despair.
So I made popcorn, and found her my DVD of the James Franco / Sofia Myles movie, and found a version of Lovespell, and we had a Tristan party. Then I got her the librivox audio version of the English translation of this same version (by Hilaire Belloc). Both of which are still not my preferred version of the tale: Belloc was a prude, and chopped out several bits of Bédier's text that he found inappropriate, but that is the version that is in the public domain, so it's also the source of the librivox audio.
Then we had a long talk about just how many versions there are, and how the movies differed from the Bédier version and she listened to it in English during her morning commute and somehow managed to ace her essay test. So go her, but boo on teachers assigning this to 16 year olds.
I may go to whatever circle of hell Dante has assigned for people who don't like great literature, but while this story itself is 11 stars out of 5 for romance and tragedy, I'd frankly avoid either of these versions like the plague unless you're assigned them.
Further cementing my place in the inferno: The 2006 movie is actually pretty good. James Franco is appropriately pretty, but he's not why it's good, it's rather despite him. Sophia Myles is absolutely luminous as Isolde, and Rufus Sewell (omg how I do love him!) portrays a King Mark who is utterly sympathetic to the point you can really understand how torn up everyone gets. Further, both Tristan and Isolde are given agency, by removing the "love potion" silliness, and giving them a real backstory. And a proper tragic ending (the Bédier version is the love potion version ,and the ending really lets everyone off pretty lightly).
I'd give a book recommendation on a better version or at least one I like better, but... seems I have read so many, I can't actually remember which one I like best. I suspect the Rosemary Sutcliffe one is pretty good though (I haven't read that one, but... it's Rosemary Sutcliffe, how bad could it be?) Another I'm going to try to hunt down is Arthur Quiller-Couch's version (he actually was Cornish too), left unfinished at his death and finished many years later by none other than Daphne du Maurier.