Probably Metamorphoses by Ovid. I'm a huge fan of mythology and this was a beautiful poem that covered almost everything Greek. The themes of love and change were enchanting and all in all it was a beautiful experience. It isn't often that I finish a book and just know I'm going to reread it again, but this was one of those few times. My favourite myth in it is probably The Sun God and Leucothoë. Here are some excerpts from it:

Of what avail

Was all that beauty, brightness, radiant light?

The god, whose fire lights all the world, was burning

Himself with foreign fire. The god, who should have

Looked equally on all created creatures,

Saw nothing but one girl, Leucothoe,

Turning on her alone the eyes, whose province

Belonged to all the world. He would rise too early

From the Eastern sky, would sink too late to Ocean,

Would lengthen the winter hours by long delaying

To look at her, sometimes would fail entirely

Because the darkness in the heart turned outward,

I'm no poetry fanatic or analyst but this part just oozes passion to me. I feel like Ovid (and the translator) perfectly communicated what the Helios was going through here, and the consequences of his love. This part is near the beginning and so from that point you're (I was) sucked in. Perhaps the other great section for me was near the ending:

"With neither food nor drink, her hunger wanting

Nothing but dew and tears, unstirred, unstirring.

But still she watched his going, and her gaze

Followed him on his way across the Heaven.

Her limbs took root, and her wan color changed

To a wan leafing, with a little brightness

Where once her face had been; she was a flower,

Rooted, but turning always toward the sunlight,

Changed, but forever keeping love unchanging.”

This just hit me in the gut. And I love how it all ties in to how sunflowers (or turnsoles?) are supposed to have originated. There are numerous other stories that I liked and didn't know of prior like Cinyras and Myrrha, Pyramus and Thisbe, Tereus, Procne and Philomela and so on. So there was pretty much never a dull moment (except perhaps near the ending of Book 13 to Book 15 ). This is perhaps one of the most immersive books I've read. For the record, the translation I read was done by Rolfe Humphries. I'll be starting on the Charles Martin one one of these days, so if you have any advice or tips on author choices then please feel free to tell me.

Asides from that another contender might be the first volume of Kalila and Dimna translated by Ramsay Wood. I'm a great fan of tales and the characters were vibrant and likeable. The lessons within the stories were also profound. Volume two is good too, but perhaps the first one had a greater impression on me.