I have frequented two Pentecostal congregation groups:
1) Assemblies of God,
2) Apostolic Pentecostals.
I had the former for church home for two years even though I never agreed with Pentecostal tenets; I enjoyed their enthusiasm in serving the Lord. I have visited congregations of the latter group many times.
Experiences have varied widely. At first, I thought, like Sgt. Fury, that things were not done "decently and in order" like 1 Corinthians 14 prescribes. It looked like chaos. However, as I observed more, I saw that for the most part, it is `controlled chaos.'
Assemblies of God that I saw vary from
i) a small rural congregation that was not much different from a Baptist church, to
ii) an urban church at an upscale city.
The emphasis seemed to be very much on `show' in the two congregations I saw from bigger towns -- the bigger the town, the more emphasis on `show.' On the other hand, the people filling the pews did not seem that much different in Christian character than most other fundamentalist/evangelical denominations.
The procedure for tongues is that people may babble `in tongues' privately at set times in the worship. You stay quiet during the sermon except perhaps a toned down `Amen' or `Hallelujah.' At times when private tongues are okay, such as during praise time, a person may start yelling what is thought to be a public tongue. The band stops, and the congregation goes silent until the yelling stops, and everyone waits silently until an `interpreter' speaks.
Assemblies of God are Trinitarian; Jesus Christ and the Holy Spirit are seen to be distinct Beings within One God. Assemblies of God are also frequently cooperative with other denominations. Also, for congregation prayer, a person is appointed to lead, and everyone prays orally for petitions listed for the congregation; when the appointed person says "Amen," everyone is to stop their prayers. This corporate prayer model is based on Acts 4:24.
In Apostolic Pentecostal congregations, there is no public `tongues'/`interpreter' thing. Corporate prayer is the same as in the Assemblies of God. Interestingly, preachers do not want a quiet auditorium when they preach. They want vociferous "Amen" and "Hallelujah" and similar, as well as clapping and standing ovation for `the Word as it is preached.' Believe me, they can yell right over it.
Dress codes are commonly quite strict, and women are taught not to cut their hair, which they believe 1 Corinthians 11 prohibits. The King James Version is the most commonly used translation, often by rule -- but not always. The most common greeting is not `Hello,' `Hi,' or `How are you?' The most common greeting is "Praise the Lord" as you hold out your hand.
They are Oneness, meaning that they believe God was the Father, then changed form to incarnate as Jesus Christ, and then after Ascension, returned to us as the Holy Spirit. This is the reason that baptism is in "Jesus' Name," and the person `speaking in tongues' is expected to be evidence of salvation. Adamance about Oneness varies: some insist that Trinitarian Christians are polytheists who are Hellbound, while others value all Christian denominations even if `wrong' on this. Adamance about Oneness baptism and tongues varies as well: some insist these are needed or a person can expect `eternal barbecue,' while others others value all Christian denominations even if `wrong' on this.
As for entirely non-denominational Pentecostal churches, one never knows what s/he is going to see and run into. When emotions lead church congregations or religious organizations, anything can happen. Some non-denominational Pentecostal churches are at least somewhat controlled; others can be very wild.
Pentecostal Bible interpretation differs from most other groups. Pentecostals seem to view the Bible as a Book primarily of promises to us.
Pentecostal groups tend to have services on Tuesday, Thursday, or both. Many also meet on Sunday afternoons. Their unusual service times enable someone like me to visit them. While I do not agree with the religious tenets, and do not always approve of the excesses, they do have an attention-getting way of reminding me to live out my committment as a Christian.