In this chapter, Gideon kills the two kings of the Midianites and launches reprisals against Israelite towns that did not support him.
This chapter begins with the Ephraimites complaining that Gideon did not invite them into his army when he gathered the original 30,000 (and later, 300) men to fight against the Midianites. Gideon responds by trying to flatter them, calling the "gleanings" of Ephraim better than the vintage of Abiezer (his family). Gleanings are the remnant grapes that are left over in a field after it has been harvested, so Gideon is basically saying, "your worst is better than my best", all because Ephraim caught the two leaders of Midian (presumably these are the military leaders or generals of Midian; their kings are captured later).
Ephraim is pacified by this response, which is interesting because it shows us (in hindsight) how significant it was that Jael killed Sisera. Indeed, the honor of slaying the leader of the Canaanites was given to a woman, just as the honor of killing the commanders of the Midianites is given to Ephraim, although Ephraim was not involved with the earlier battle.
Gideon's response to Ephraim is generally considered a positive example from his life, because he answered them wisely to assuage their wrath. This is juxtaposed with a later story in Judges where, in a similar situation, a different judge will give a much less wise response and things will go worse.
After this, Gideon and his men pass by two Israelite towns, both of which refuse to help him. This is yet another example of how Israel is paralyzed by fear. Even after Gideon won a major victory and had destroyed 90% of the Midianite army, two towns (both in Gad, east of the Jordan) refuse to help Gideon because they are afraid of Midianite retribution if Gideon is later defeated.
Still with the same 300 men as before, Gideon defeats the Midianites again (this time reduced to 15,000 men), and just as he promised he goes back and scourges the leaders of Succoth, while destroying the town of Penuel. When he meets the two kings of Midian, he commands his own son to kill them and his son is too afraid to do it. While verse 20 says this is because "he was still a youth", it is also probably because of a general fear of the Midianites like we have been seeing not just in this chapter, but also chapters 6 and 7.
After killing the two kings, things with Gideon start getting a bit more complicated. The people ask Gideon to rule over them, and he refuses. On the one hand, Gideon says, "the LORD shall rule over you", which seems like a pretty godly opinion. But on the other hand, he turns around and creates an idol for his hometown, contrary to the second commandment.
I think there are two interesting dynamics going on here which I will address in turn. The first is Gideon's faith. Gideon constructs an ephod, which the people of his town treat as an idol. This is somewhat peculiar because the last time we saw an ephod it was part of the high priest's garment, but in this case Gideon's ephod somehow became an object of idolatrous worship itself. I don't exactly understand why they would worship an ephod, but from what I can tell ephods are commonly associated with household gods (see e.g. Judges 17:5, Hosea 3:4). Possibly Gideon also had household idols, on which he puts the ephod of gold.
But that's not the interesting part to me. The interesting part is, why is Gideon worshiping an idol when he was the selected champion of the LORD? I really think this is one of the most confusing parts of Gideon's story. His fear I can understand, and the LORD reassures him many times to get him over it. His victory over the Midianites was great, and then he makes the very pious statement, "the LORD shall rule over you". And then he makes an idol which becomes "a snare to Gideon and his household". In part, I wonder why the LORD would choose a leader for Israel whose heart would fall into idolatry. All of the previous heroes of the faith have been so strong and reliable, like Abraham or Jacob or Moses or Deborah. I mean sure, some of them struggled with doubts or anger or other problems, just like Gideon struggled with his fear, but it just seems unusual for a judge to fall into idolatry. To be fair, Aaron also was involved with the idolatry of Ex 32, and Aaron was the high priest. But he got rebuked for it, some people died and they moved on. In this case, after Gideon made the idol it seems to cast a lingering shadow over Gideon's family as there is no sign they ever stopped worshiping it.
For everything he accomplished, you want to like Gideon. But this ending to his life's story is so bitter it is hard to feel positive about him. I guess what I can say is that he accomplished great things, but like many people who do great things, he had some real problems too.
The second interesting dynamic is how the Israelite people seem to be inclining their hearts towards a king. Although Israel has had supreme leaders for a while (Moses, then Joshua, then the judges), this was not a hereditary system. With Gideon, they ask for "you, your son and your son's son" to rule over them, establishing a de facto kingdom under Gideon. Deuteronomy 17 predicted that the Israelites would ask for a king, and generally seemed okay with the idea as long as it was a king appointed by the LORD, not a foreigner, and who honors and follows the law of Moses. It wouldn't have been wrong for Gideon to become king of Israel, but I don't think his refusal is bad either. What we can see is that the Israelite people are seeking a king to protect them from the hostile nations that lie on every border (having warred against Moab, Ammon, Amalek, Midian and Canaan, there doesn't seem to be a friendly nation anywhere to be found).
Lastly, Gideon has 70 sons through his "many wives", which seems like it contradicts the command in Deut 17:17 against doing just that. Although Gideon refused the kingship, he is still effectively the leader of Israel at this point; how else could he afford to feed 70 children and numerous wives and servants if he wasn't also extremely wealthy? So I wouldn't say that this is a direct violation of the law, but it's pretty close. I think it's fair to say this is another sin on Gideon's part, marking yet another poor conclusion to what was a great beginning.
To the surprise of no one, the Israelites return to idolatry after Gideon dies. In the next chapter we will find out what happens to Gideon's legacy.