Lonely Hearts is lifted above the average crime thriller through the excellent performances by the cast. The movie alternates between the detectives who are on the trail of the Lonely Hearts killers, played credibly by John Travolta & James Gandolfini, and the bloody spree of the killers' Martha Beck [Salma Hayek], and Fernandez [Jared Leto].
The detectives are well-played with a sub-plot involving John Travolta's character grappling with the case as well as his own personal problems [having to do with his strained relationship with his son, as well as his affair with a colleague played by Laura Dern]. However, the real action and drama comes from the performances by Salma Hayek, and Jared Leto as the cold-blooded killers. Hayek's performance is especially riveting, and her Martha Beck comes across as unflinchingly evil whilst besotted with her lover.The portrayal of the killers in this movie though well-acted, is not an altogether accurate portrayal of the real-life criminals [the real Beck was obese, not a sultry temptress as embodied by Hayek].
On the whole however, this is an eminently watchable crime thriller with credible performances all-around. A worthwhile addition to the genre.