Overall, for me it was better than the first season but not as good as the second and third seasons. David Eick is very solid on-set producer who's done some great work, but I just don't think he's as good of a writer or a showrunner as Remi Aubuchon.
One thing I appreciated about the finale, especially the first hour, is that it brought the show back around to being a family drama. For the first time all season, Lexi was used a character rather than a plot device, and I thought Noah Wyle and Scarlett Byrne did a nice job playing off each other. The Masons are a pretty functional, low-drama bunch, so having an estranged parent-child relationship (however utterly bizarre the circumstances) gave Noah Wyle different notes to play.
I had to think a little about 2001 with the finale to this season. Does this mean Tom will be an esphini convert?
Yeah, there were definitely "2001" overtones to that final sequence. But, given the reflection we saw in the mirror, I don't think he was rescued by the Espheni. Rather, I think the alien we saw, with all of its limbs, is what a skitter looks like before it is skitterized.