Tower of God is a webcomic that follows the adventure of a boy named Baam as he gets wrapped up in a quest to ascend God's Tower to escape the dark underworld he starts off in. He chases after Rachel, a girl who wants to see the outside world beyond the top floor of the Tower.
The strength this series has is the world-building established by the first season (the test floors). You get a good depiction of the Tower's setting, and the characters are established well-enough (some, like Hatsu, were bland) to get to know these characters, and wanting to see how these characters grow as they rise through the Tower floors.
The second season (floor 20 and up) is, more-or-less, the same, except that it was, basically, a complete reset, and the characters introduced here just aren't as interesting as the group Baam interacted with from the first season (Horyang is, perhaps, the most interesting so far of this bunch).
The second season also develops a severe case of slow pacing issues where it starts to feel like things are taking forever to get done; probably because at this point, the cast of adventurers are so large that the author is trying to give every character a bit of time in the limelight. The Workshop chapters in particular takes quite awhile to get done, and there's hardly a good payoff for the amount of time spent in this saga.
All in all, this series has its highs and lows. If you're put off by the first season, then you most likely won't grow on the second.