This 2005 Cadillac XLR-V belongs to the main character called Shark:

http://www.imcdb.org/vehicle.php?id=167776

Do you have any information on which episode this was from, or a 1-5 star rating of the vehicle's role ?

It´s season 1, episode 12. It´s a CTS-V (the front mesh grille is visible in a scene and there is a "V" on the rear. As yet I only saw that car in episode 12. It´s driven by District Attorney Investigator Isaac Wright (a former LAPD-Cop) but due to the conversation the car seems to belong to Sebastian Stark. I have no clue whether the car will appear in further episodes. So far I´d say two star.

you mean XLR-V I guess

Sure! Cadillac's mixture of letters confused me (since I own a CTS and I am no more young at all this seemed to be inevitable).

You can add another star if you like, because in episode 14 the XLR-V appears again, driven by Stark himself. As I supposed he owns the car.