Pärt leans towards a form of minimalism, which not everyone likes. Some of the works I personally lean towards are:

* "Cantus in memoriam Benjamin Britten": https://www.youtube.com/watch?v=bvfvO3dJqFY

* "De Profundis": https://www.youtube.com/watch?v=0vOSKaKJ1QY

* "Te Deum"† (~30m): https://www.youtube.com/watch?v=jNxbT0MESTY

* "Fratres" (for cello and piano): https://www.youtube.com/watch?v=v4XMjsYeMig

* "Fratres" (for violin and piano): https://www.youtube.com/watch?v=7PS5QMsGaRw

* "Fratres" (for violin, chambre orchestra, percussion): https://www.youtube.com/watch?v=i9I-6QPT8Is

* the Tabula rasa album: https://www.youtube.com/watch?v=7YqF69HLkj8

If you're going to listen to a choral work, it's worth looking first for recordings by the Estonian Philharmonic Chamber Choir, as Pärt often collaborates with them (sits in on performances, recordings; he's Estonian himself so there's a 'cultural collection').

† On a historical note, the "Te Deum" is one of the earliest Christians hymns we know about (and that is still used), apparently dating back to before 500 AD: https://en.wikipedia.org/wiki/Te_Deum

https://youtu.be/T2WuzKeDx8U

https://www.youtube.com/watch?v=jvXy69eF__Y

Prior to this he had composed in the dissonant, serialist style that was expected of "serious" art music in the middle of the 20th century. This was the first piece where he broke with the contemporary style and introduced his unique "tintinnabuli" style.

If you have even a basic familiarity with music theory it's worth taking a look at the structure of the piece because it's surprisingly simple for the effect. As the right hand plays the melody, the left hand simply plays notes from a b minor chord, with the particular note being whatever is just beyond one octave below the note that the right hand is playing. However there is one exception towards the end where the left hand plays a C# instead of a D as it would be expected to, and this marks the climax of the piece.