Taproot Theatre gets a number of things right in its staging of Big River, the 1985 musical that follows Huckleberry Finn and his runaway slave companion Jim as they raft down the Mississippi River. First, the notion that Big River and summer go together like picnics and watermelons is spot-on. With an eminently hummable score (from "King of the Road" tunesmith Roger Miller) and an evergreen morality fable (Mark Twain's original text is tailored for the show by William Hauptman), it's easily the most marketable summer fare since Oklahoma! Second, Taproot's guiding lights understand their crowds will forgive the cutting of a corner here and there when they're presenting theater on a budget with a largely inexperienced group of players stomping the boards.On the whole, this Big River is a friendly and earnest affair, but be warned, as this incarnation can lurch unexpectedly from amusement into a Big Muddy of amateur antics. The show pre-sents a number of opportunities for the performers to chew the scenery, and all too often director Karen Lund fails to drive home the cardinal rule of ensemble acting: All the players must at least appear to inhabit the same universe—no matter how far that environment is removed from ours. It's no less disorienting than seeing a character from Star Wars or High School Musical wandering through a Harry Potter tale.Since Big River is first and foremost a musical, it's worth mentioning that things go best here when the cast is engaged in song. The late Miller, who had untapped range as a composer until he tackled this project, gave them plenty to work with: the signature witty ditties "(How About a) Hand for the Hog"; Miller's take on Descartes' "I think, therefore I am," which appears in song as "I, Huckleberry Me"; a bluesy treatise on "Guv'ment," a weepy country ballad, and a pair of slave spirituals. The ensemble at Taproot delivers them with gusto, and the opening-night audience responded with enough whoops and hollers to make you think you'd stepped into a Saturday-night saloon dance during the Gold Rush. In the quieter moments, the slave singers' laments will pierce you to the core.If all of that is right, then what could possibly go wrong? Well, for starters, this Huck Finn (Robbie Fowler) spends the evening wrestling with a sibilant "s" that he just can't shake. That's distracting. Several cast members can't resist mugging for the back rows, when the farthest seats are less than 30 feet away. And in solo moments, even the best singers (most notably Geoffery Simmons, an inspired choice for Jim) aren't always projecting enough to make their lyrics plainly understood.So let's lay it out, plain and simple: If you're looking to hear the best Big River possible, buy a copy of the original cast recording and let your imagination fill in the blanks. If, however, you're looking for a fun night out with a scrappy crew of eager-to-please performers, by all means grab a ticket to Taproot. Big River is as American as Sousa, apple pie, and Norman Rockwell, and if you've never heard "Waitin' for the Light," "River in the Rain," or "Muddy Water," go anyway. There won't be a better batch of showtunes on stage 'til fall.