Adam Rapp’s “Finer Noble Gases” is one of those funny creatures: a mediocre play that’s exceedingly entertaining. Four roommates watch TV or stagger in a daze, utterly zonked on drugs. Reality blurs as they choose between their pink, blue and yellow pills, shadows of their old life appearing in the corners. Their crazy-junkie antics are banal but very well performed, particularly by the playful-quirky Paul Sparks (as Chase) and Michael Chernus’ hulking Lynch. The roommates’ spacey reality is interrupted by the arrival on the scene of a neighbour, Gray, played by Connor Barrett. After a hilarious telephone conversation with Chase he’s invited upstairs, where the plot-thread fizzles. There are more than enough gags to maintain momentum, however, and while by the end of the play there’s been little emotional revelation (and apart from a scene with a robot, little poignancy) – the audience is filled with smiles. In a strange but somehow fitting move, the last quartet of the show is a full-blown rock concert: the set is cleared, the actors strap on guitars, and Less the Band perform a genuinely excellent set of My Morning Jacket-like indie rock. It’s a warm, resonant closing note for a show whose heart is otherwise rather vague.