PikaChu

Without really knowing what aspects of a drama make it enjoyable for you, its hard to really say and I don't want to spoil too much either in case you choose to continue. I would say that while NIF settled in better for me after ep 6/7 (understanding the background) and started to pick up, probably between 19-25 is when you start to see how deep the conspiracies run, how power balances can be tipped, and the main characters' resolve really firming up. Since this show involves so many people scheming for their own interests, there will be some slow spots as they introduce the relevant pieces for that piece of the plot and this tends to happen more in the 1st half, but if as you're approaching the halfway point of the drama and it still doesn't grab you at all, it just may not have the elements that interest you. If as you're approach that mid-way mark and it seems to get better for you, you like how the plot is unfolding and the characters' growth then keep going because unfavored prince Jingyan cannot stay low-key nor stay unfavored forever if he wants a shot at the throne. For me it gets better when he finally resolves to fight for this and starts to confront more directly (whereas the earlier episodes he is more passively nudged by Mei Changsu to follow his guidance).