To answer your question, I will present the four differentiators of “mainstream” orthodoxy vis-a-vis “modern” orthodoxy. However, none of the four has anything to do with Halacha as modern orthodoxy maintains, nonetheless, that Halacha reigns. What you may be referring to is the unfortunate failures of some who practice modern orthodoxy.
1. The role of the Rov: mainstream orthodoxy views the Rov as a life mentor who is often asked questions about marriage and business and child rearing as much as Kashrus and Shabbos. This differs in modern orthodoxy which views the Rabbi as strictly a religious figure to answer halachic questions.
2. The State of Israel: Modern Orthodoxy believes that the Medina is “ikvisa d’meshicha” and therefore requires accepting the bad with good as the bad is only temporary until Moshiach. Mainstream disagrees and believes that we must fight every attempt of anything that “smells” of being contrary to Torah to the point of harog v’lo ya’avor. This results in religious Zionism being synonymous with modern orthodoxy, while the mainstream believes that the term “religious Zionism” is an anachronism.
3. Secular Education: Modern orthodoxy believes there is an inherent value of achieving success in secular education as doing so makes one worldly and “educated”. Mainstream orthodoxy disagrees and views secular education is only as important as one’s need for panosso. Therefore, any other time spent on secular education is being b’tul Torah at best and blasphemous at worst.
4. Women’s Roles: Mainstream Orthodoxy believes that we must follow the longstanding mesorah, articulated by the Chofetz Chaim and the Ger Rebbe when questioned by Sarah Schenirer. This dictates that women and girls should largely focus on Torah Shebichsav and Halacha. Further, while women do you get jobs and may have careers, their focus remains largely on the homefront. Modern orthodoxy believes that, as the world has changed, women must be intellectually stimulated by opening up all forms of study, across the board, and allowing, even encouraging, women to seek careers that satisfy their intellectual quest.
In closing, I hope I presented these ideas in such a way that the reader will not be able to know my personal beliefs on the subject.