Few contemporary playwrights embrace the “one for me, one for them” trajectory as starkly as Enda Walsh. The prolific Irish writer/director alternates between loony, incisive chamber psychodramas (Misterman, Ballyturk) and loony, broad crowd-pleasers (Once, Roald Dahl’s The Twits, Lazarus) with a panache that marks him as a distinctly 21st-century artist, hard to pin down and adept at re-invention. His latest St. Ann’s Warehouse transfer, Arlington, sits firmly in the former camp, stretching his trademark idiosyncratic investigation of the effects of isolation on wild, creative minds toward exciting new abstractions.