The second season of TNT’s “Snowpiercer” improves on the lackluster first year by giving the show a much-needed antagonist and opening it up in terms of world-building and depth of character. Having said that, it still succumbs to a serious midseason sag in terms of momentum and increasingly feels like a transitional piece of the track in terms of the entire arc of this show, playing with themes that it won’t really be exploring until a third or maybe even fourth season. Most of all, it’s a program that’s too often cluttered with characters who constantly say what they need and what they’re going to do to get it. Strong new performances, a series-best pair of episodes to start the season, and a great showcase for one of its best stars in episode six make this 8-episode run the best of “Snowpiercer” yet but it’s still a show that hasn’t quite found its track.