Chapters 1,2 :
The first two chapters of Judges show that Israel did not obey the command to kill all the inhabitants of the land (Deut. 20:10-18); This initial disobedience provides the backdrop against which the rest of the cycles of sin in Judges are placed.

Chapter 2 :

2:1-5 - God Rebukes Israel (for not killing inhabitants)
The angel of the Lord : Possibly a theophany (an appearance of Christ in the OT) or the Holy Spirit (not much support for this), but most likely an angel delivering God's Message.
Gilgal : This was the camp of Israel for the timeperiod covered by Joshua. It was on the western border of the Jordan, near Jericho. Joshua set up the twelve pillars of stone at Gilgal after crossing the Jordan; that the Angel came from Gilgal could be reminding the Israelites of God's faithfulness (contrasted with their disobedience).
2:6-10 - Israel obeyes for the length of Joshua's legacy
2:11-15 - Israel embraces Baal/Ashtaroth; God delivers Israel to their enemies.
2:16-23 - The cycle of Judges definied: Sin -> Oppression -> Repentance -> Deliverance through Judge