Having been in many churches throughout my life, I never knew what real fellowship was until I discovered small groups meeting either in homes or within the church structure.
There is a type of fellowship (more of a social nature ) with all the potlucks and worshiping together in a church, although when I was young, it wasn't really worshiping to me to sing the song out of the hymn book (all 5 verses), and try to find out whether your best as an alto, soprano, tenor, etc. It felt more like telling a story about Jesus, or an invitation to come to Him. There was no honest sharing with each other the struggles they were going through or what they needed prayer for.
But I found a depth of fellowship in small groups or 8 or 12, where there still was teaching (followed by discussion) and prayer. Yet, the people opened up and shared their lives honestly, asked for prayer and were prayed for right on the spot. Even the ones who needed healing were ministered to through prayer by all the others in the group. Even the worship felt like Jesus was right in the middle of the room, and we were caught up in His presence. A time of just silence before Him felt good. And how special it is to pass communion to each other around a room. Great bonding.
Guess you can tell, I believe "good things come in small packages".
But, on the other side of the picture, I have attended retreats where 100 to 150 people are singing praises with overflowing hearts, and it sounds a little like it must in heaven. That's a good thing, too.