“Stranger Things 2” is big. Everything about it is big. Its story is big, its emotions are big, its music cues, homages, and characters are all big, big, big. With an additional episode, a handful of new faces, more money in the budget and inflated ideas to match, the sequel season to Netflix’s breakout original series is a conscious move to broaden its scope and lengthen its story. Season 2 takes a while to get going, and there are more growing pains other than additional setup, but the first season’s lively spirit perseveres for a largely thrilling adventure that’s hard not to enjoy.