Rashi: In all of Tanach, it is complaint and lamentation, like one who groans from his heart and screams 'Ahah.' A minority of them are an expression of screaming, e.g. "Hoy Hoy v'Nusu me'Eretz Tzafon" (Zecharyah 2:10). The Targum is Achlu, an expression of announcing. It is proper to scream over "Goy Kadosh" (Shemos 19:6) that converted to be "Goy Chotei"; the nation about which was said "Am Kadosh Atah" (Devarim 7:6) turned to be "Am Keved Avon." Also refer to 8:8:1:1.

Radak: It is calling out and screaming, whether amidst mourning or to be heard. Yonason translates it to be an expression of mourning, like Oy. He translated 'woe to a nation that was called Am Kadosh, and they sinned.'

Malbim: It is a word of calling out.

Rashi: The sin is heavy (severe). Keved is a noun; it is Samuch to "Avon." Radak - Keved is To'ar (descriptive). Its grammatical form is like Melech, Eved.

Malbim: The Navi ascends levels [describing their sin]. Not only are you Goy Chotei (Shogeg). You are Keved Avon (Avon is Mezid). He also describes the nation in ascending levels - Goy, Am, Zera, Banim. The sin of someone more esteemed is greater, and is punished more.

Rashi: They used to be "Zera Berach Hashem" (61:9) and "Banim Atem la'Shem" (Devarim 14:1); they reversed to be "Zera Mere'im, Banim Mashchisim."

Radak: They are not seed of Mere'im. Rather, they are seed that do evil to themselves, via their evil deeds. Similarly, they are Banim Mashchisim - they ruin their ways.

Malbim: Not only do you sin occasionally. Goy Chotei (Shogeg). You are Keved Avon (Avon is Mezid). "Mere'im" is an adjective; it shows that they constantly did evil. And it was not for benefit, rather, "Mashchisim" - he merely ruins his Nefesh.

Malbim: Had they not totally abandoned Hashem, they would have been like the Shomronim - "Es Hashem Hayu Yere'im v'Es Eloheihem Hayu Ovdim" (Melachim II, 17:33). However, they totally abandoned Him.

Rashi: They angered. Malbim - this is worse than one who just wants to cast off the yoke. They disgraced Hashem and wanted to anger Him!

Radak: He was sanctified among them via His wonders and vengeance against their enemies - and they abandoned Him!

Rashi: Nezirah is always an expression of separation - "va'Yinazru mi'Kodshei Vnei Yisrael" (Vayikra 22:2), "Nazir Echav" (Bereishis 49:26). Radak - they separated from Hashem, and turned back from His Avodah. Nazoru's grammatical form is like "Yacholu" (Shemos 8:14).

Radak #1: They turned the back of their necks to Hashem, and not their faces - "va'Yihyu l'Achor v'Lo l'Fanim" (Yirmeyah 7:24). Yonason translates there, they turned their backs to My Avodah.

Radak #2: Nazoru is Niphal, like "Shadayim Nachonu" (Yechezkel 16:7); "Nasogu [Achor]" (below, 42:17); the root [of Naziru] is Zar.

Radak citing Targum Yonasan: Due to their evil deeds. (This refers to the punishment, and not the deeds.)

Malbim: They reverted from serving the ancient G-d to serving other gods. Had they not served at all, one could have said that love of idleness and freedom turned their hearts away from Hashem. However, they thought that serving idols is better than serving Hashem. This sin is too great to bear, for it is harder to serve idolatry than to serve Hashem. They burned their sons and daughters to idolatry, and it was not a burden to them, but they wearied from Avodas Hashem!