Why does it say "v'Gam Eleh ba'Yayin Shagu"?
Sanhedrin 111b:Midas ha'Din asked, why are Tzadikim with these Midos (refer to 28:5:3:1) treated better than others who do Your will? Hashem answers, the others (were not such Tzadikim;) also stumbled in wine.
Rashi: Also those who judge and fight wars in the generation, i.e. the best of them, erred in wine. Now, there are no good ones among them.
Radak: Also Yehudah and Binyamin erred with wine, in the days of Achaz. Also they were worthy to be exiled; they were not, for a king (Chizkiyah) was destined to rule over them who would return them in Teshuvah.
Malbim: This refers to the rest of His nation and it Giborim, i.e. Shevet Yehudah. They should have learned a lesson from Efrayim, who were stricken through wine!
Why does it add "uva'Shechar Ta'u"?
Malbim: First they erred slightly via wine. Later, they erred greatly via Shechar, i.e. intoxicating wine 1 .
If "Yayin" does not intoxicate, why did they err through it? Perhaps it intoxicates a little. (PF)
Why does it mention "Kohen v'Navi"?
Radak: It is upon them to teach the Torah. They erred like [the others], through drinking and pleasures. "Navi" refer to false Nevi'im. They deceived them, and permitted to them pleasure, and said 'you will have Shalom. Do not fear; do what you want.'
Radak citing Targum Yonasan: Navi is Safar (a Talmid).
Malbim: It is upon them 1 to teach the Torah.
Did the wine swallow them?!
Radak: They were ruined through drinking too much, and strayed from the proper path from much strong drink.
Malbim: The Navi's power of Nevu'ah and imagination were destroyed.
What is the meaning of "Shagu ba'Ro'eh"?
Rashi: They mocked the words of the Ro'eh (Navi).
Rashi citing Targum Yonasan: [They erred in] eating delicacies that they saw delight in them.
Radak: Ro'eh is a name; its grammatical form is like "Yoreh [u'Malkosh]" (Devarim 11:14). They erred about the Nevu'ah of the true Nevi'im, and did not follow them.
Radak citing his father: They erred even about something that the eye can see.
Malbim: [Since their Nevu'ah and imagination were destroyed,] they saw false visions and seductions.
Why does it say "Paku Peliliyah"?
Sanhedrin 111b: Judges who judged when they were drunk will go to Paku, i.e. Gehenom - "this should not be for you l'Fukah" (Shmuel I, 25:31). Peliliyah implies judges - "v'Nasan bi'Flilim" (Shemos 21:22).
Rashi: They gave wrong judgment. Paku is an expression of [stumbling], like "u'Fik Birkayim" (Nachum 2:11) and " l'Fukah." Radak - this refers to the Kohen and Navi, who should judge them true Mishpat.