Go to enough dim sum joints and the same-old same-old gets old-old. Another Styrofoam-tasting deep-fried crab claw? Sigh. Another central commissary sesame ball? Must we? That's why JunBo, the new mega-ambitious, mega-sized Chinese place that took over the old Chi-Chi's space on Nicollet and I-494, is such a delight. They have so many cooks, so many carts, and so many mouths to feed (the place seats 400) that same-old, same-old simply gets drowned out in the tidal wave of fresh, new, and adventurous that the kitchen sends out. For instance, have you ever seen bitter melon fritters, bright green as candy, with black-gray pureed centers? Ever seen dumplings meaty with boiled peanuts? Giant shrimp dumplings topped with checker-sized discs of steamed scallop? Fried ribbons of shrimp paste made chewy and jerkylike? If you've never seen those perfect little treats, you will if you occupy one of the many, many, many tables at JunBo, where they serve the best dim sum in town, and the most frequent: It's available weekdays from 11:00 a.m. to 11:00 p.m., and weekends from 10:00 a.m. to 11:00 p.m.