Don't expect a sugar rush from 'Charlie and the Chocolate Factory,' the new musical that opened at the Lunt-Fontanne Theater on Sunday...This big but tentative show - which features a book by David Greig and songs by Marc Shaiman and Scott Wittman - doesn't burst with flavor of any kind, at least not during its exposition-crammed first act. Only in its second half does the show acquire a distinct taste, and it definitely isn't confectionary.