I'll say this because it sounds like you really don't know. This anime is an adaption of a long running light novel. In fact, it's the longest continuation novel by a single author to date, with 126 volumes. Unfortunately, the author died in May 2009 (hence the dedication at the end of the episode), and the series cannot be finished.

As for why I didn't like this ending, it seems that they decided to put a lot of effort in showing the drama presumably leading up to the next season. That's all fun and games, except for one major problem. Why did they make several of the main characters fall below their beliefs? Characters in an anime have to be consistent to be interesting, and this was NOT consistent with how they acted through the rest of the series, particularly Istovan.

It must have been just 3-4 episodes ago that Istovan declared that he would become king by his own right, without using Rinda to become his "Princess of Light," and an automatic path to becoming king since she is already royalty. Why, now, is he begging Guin to help him become king? He doesn't believe that he can do it by himself, but that's a load of **** because the whole series he claimed that he believed in his own destiny, and that his destiny was to become king. In the beginning of the series, he said that he would become king, even though he was just a no-name mercenary. Why doesn't he think that he can do it anymore?

I also don't know why Guin was scoffing at fate when he was talking to Istovan. That's not something that he should say because he heavily believes in his own fate and he follows that. Why was he implying that following your destiny is the wrong thing to do in his talk to Istovan? Enough ranting, I hope you get my point. The characters lost it during this episode.