How does the Orthodox Church view the Roman Catholic Church? How does the Orthodox Church view the Roman Catholic Church?

Specifically


Does she consider RCC herectical? In what matters?
Does she consider RCC priesthood and sacraments as valid?
Does she allow her children to to attend RCC Mass and receive the Eucharist or the Sacrament of Penance?
Yes and no. The Catholic Church was initially considered by the Orthodox Church to be heretical, but as time passed and the term began to have strong negative connotations, the term was changed to heterodox, at least in official discourses. However, hardliners are still using the term heretic. In what matters? Well, the first one would be the filioque controversy. Search for it on this site, it's discussed in numerous threads. Other issues like the Easter date, celibacy of priests, unleavened bread used for the eucharist, withholding the Holy Blood (eucharistical wine) from the laity, using the organ in church music, papal primacy, papal infallibility etc. are considered by the Orthodox Church to have no basis in the Holy Scripture or the Holy Tradition (teachings of the Church Fathers) and thus they are not orthodox, but heterodox.
I come from a catholic family so I was baptized catholic. I converted to orthodox christianity a few years ago, and the conversion did not include a baptism. This is because the catholic baptism is considered valid by the Orthodox Church. Both Churches have apostolic succession (by laying on of hands) so both orthodox and catholic priests received the Gifts of the Holy Spirit on ordination. Baptisms performed by other denominations are not considered valid (especially the ones from the non-trinitarian denominations, because a person has to be baptized in the name of The Father, The Son and The Holy Spirit). Eucharisty on the other hand is not considered valid. Furthermore, it is strictly prohibited to give the Holy Communion to non-orthodox people. I'm not 100% sure, but this should be the same in the Catholic Church also.
Attending Mass in other churches is not prohibited. In both Orthodox and Catholic Christianity the reason one calls a priest father is because he is one's spiritual parent, guiding him in his spiritual endeavours. Penance should not be just an enumeration of your sins, but also a desire to not repeat them and asking the priest for guidance, which he provides based on the teachings of the Church. It would be a kind of nonsense to be orthodox and seek guidance from a catholic priest (offering advice based on catholic teachings) or viceversa. If one feels like doing so, for whatever reason, then why not convert?


I'm romanian, and most of the information in this answer I learned from the writings of romanian orthodox monks, priests and theologians (also some greek, russian and Church Fathers writings).