Here are some English-language articles:
The Kingpins - Lengthy but pretty comprehensive article that lays out the relationship between the PRI, Enrique Pena Nieto, and the narcowar, as well as the influence drug violence has had upon Mexican voters.
Mexico’s Election: A Vote For Peace, A Plan For War - Offers some background regarding the origin of #yosoy132 and American interference in the elections.
Mexico’s Youth Uprising - Written just before the elections, capturing the mood at that time.
Raped, Beaten, Never Forgotten - Information about the widespread sexual assault of women in San Salvador Atenco, which occurred under Ernesto Pena Nieto’s watch, and is one of the biggest contributors to outrage against him.
Reports of gift card payments… - Concerning the gift cards to Mexican supermarket chain Soriana, which were used to buy votes for the PRI, and the origin of the the numerous Soriana references in the protests.
(I do not claim that the information in these articles is 100% accurate or free from contention, but they should give a sufficient understanding of the factors at play here.)