1. Generally, with a given congregation on this website, there are two numbers given - one is membership, and the other is average attendance. The trend I saw was that attendance was in general 1/3 of the total reported membership of these congregations.
2. A second thing I have noticed with many of these huge "megachurches" is the ungodly number of staff members. Some have upwards of 100-200 paid professional staff, and the ironic thing is that these staff members often are designated "pastors" for some weird reason - if one is responsible for cleaning toilets, they are "Pastor of Plunger Control" or something (that is facetious, but it shows that there is a validity to the concern).
3. A third observation is also demographic in nature - in many of the cities these supposed "big" megachurches are, there seems to also be social issues such as rampant crime, drug abuse, homosexual activity, etc. Given the low attendance and overstaffing of many of these same congregations, it shows a sort of inconsistency in witness.
There are some other less-important but still pivotal things about these big congregations which also stand out. Many of them embrace a "contemporary" worship atmosphere (rock bands, pastors giving motivational talks, etc.). Also, many of them eschew usage of the denominational heritage they identify with - if they are "Baptist," for instance, they refuse to use that name in their congregational name. Thirdly, there are other semantic issues - terms like "missional," "relevant," etc. - that seek to almost deceptively downplay what these congregations are really about. However, there is one standout phrase I want to talk about briefly that really sheds light on who and what these congregations stand for, and it is an odd statement.
I have seen more than my share of these big congregations boasting that "they are different from everyone else," yet when you visit about four or five of them that say that, they are exactly the same - loud rock bands, dimly-lit sanctuaries, etc. So, what is so "different" about them? In reality, the only difference they all have is departing from a lot of established Christian practice, and in doing so they are slowly secularizing. The fact is these congregations, no matter how "different" they say they are, in reality they are cultural conformists - they ape each other, and they also ape the secular culture around them, so there are no true differences about them. That of course leads into what the whole of my discourse is going to be about, and I want to start with a personal story.
Some years ago, my wife and I attended a congregation of a large Pentecostal denomination in a nearby town that met in the living room of the pastor. The pastor himself was young, and he was also one of these early "trendy" pastors who wanted to supposedly "reach everyone where they were." In doing so, there was no structure to the church services, and chaos rather than reverence reigned within the life of the church and its pastor - it was not uncommon to see kids running around unattended, screaming to the top of their lungs, and the pastor himself preached dead messages that sounded like a combination of Oprah Winfrey and Joel Osteen (if there is a difference!). It came to a head on a Palm Sunday one year, when instead of observing one of the holiest of seasons in the Church, this pastor decided to turn it into a day of volleyball and hot dogs in his backyard. I was appalled, and refused to attend that day as instead I went to a local Methodist church within walking distance of our house then and had a much more fulfilling experience. I of course was eventually condemned for that, and told I was essentially "bound by tradition" and the pastor's wife even targeted me for a "deliverance session" which was designed to make me over in her image, which I am happy to say didn't work at all. Several months later, that church disbanded, and in time so did the pastor's family - he and his wife divorced, and he was later defrocked by his denomination. In time, his wife continued in ministry, and after some years she actually grew up somewhat and I am friends with her today, although I don't necessarily see eye-to-eye with her ideas on several things. But, at least it is respectful. I tell that story to illustrate that trying to be "trendy" and "relevant" often is not God's ideal - Tradition exists for a purpose, and it is not necessarily bad despite what some iconoclastic Evangelicals say. I will talk more about that in a moment, but before I do so, I will always and ever be an unapologetic traditionalist - being a traditionalist has served me well personally, as it has encouraged growth and responsibility. But, more important, it is about following an order that Jesus and His Apostles set at the very beginning of the Church itself, and while some minor things may be updated and developed over centuries, the basic core of faith, order, and practice will always be Apostolic in the truest sense. That being said, let's address the apparent iconoclasm of today's "megachurch" and show how in its quest to be "different" it is in reality deficient.
The first thing I want to do is a little lesson from St. John of Damascus. St. John (676-749) was a saint of the Antiochian Eastern Christian tradition who was alive at around the time Islam was starting to become a threat. While his family were originally subjects of the Byzantine Empire, when he was quite young the area they lived around the city of Damascus in present-day Syria fell to the Islamic invaders in AD 635. and when he was older St. John actually served the court of the Ummayid Caliphs that ruled the area. Although later becoming a monk, St. John knew the inner workings of the Islamic government. At that point in time, Christians were still in considerable numbers, and in order to transition power, Islamic rulers often relied on Christian and Jewish (and in some regions, Zoroastrian) officials to administer their territories, so this was not uncommon. It was only in ensuing centuries that Islamic aggression, as the religion grew and spread, began to persecute and suppress other religions. It was in this environment that St. John was raised, and it had bearing later on one of his most important works, Three Apologetic Treatises Against Those Who Decry Holy Images, which was directed at both the Islamic radicals of his day as well as the efforts of the Byzantine Emperor Leo III, who instituted the Iconoclastic Controversy that caused issues for the Church for some time (information taken from https://en.wikipedia.org/wiki/John_of_Damascus, accessed 5/4/2017). What he wrote though is of significance for this day and age, when a new type of iconoclasm in many "megachurches" has created what my Theology professor at Franciscan University of Steubenville, Dr. John Bergsma, calls "spiritual amnesia" among them. It is at this point I will reference St. John's material to the best of my ability to illustrate my point.