I have read couple of negative reviews (a persons funds suspended because he was dealing in US illegal financial scheme HYIP) and multiple positive reviews about CoinPayments.net

I am using this merchant payment gateway for a few years already.

Positive:
- they are active adding new cryptocurrencies so mertchant can accept quite good amount of them. It can be automaticaly or manualy withdrawn to your external wallet
- they withdrawn within minutes amounts like $2000 (Late summer 2018-2019)
- they offer alot of billing system modules to integrate their payment gateway
- their support is quite fast, but it waste a bit of your time by adding robot reply which you have to reply in order to reopen the ticket

Negative:
- maybe $10,000 transacted will trigger KYC (requirement to send them documents of identity etc.)
- a bit time consuming to submit support request (idiotic bots reply and close your ticket to waste your time)
- they does not bother describing various site functions, for example "Quick POS" menu. There is no link to description how it can be used. They say you need "SYS" to send out cryptocurrency, but they are not saying what is SYS and how much one need for particular transactions. The support is ignorant when i told them about this in early 2019.

VERDICT: it is quite good if you have no problem submitting your personal documents to them (KYC)

This is unbiased review. Written around 30/8/2018 and updated in 2019. I have been using bitpay & bitstamp previously (stopped due their ridiculous KYC and documents hunger), coinpayments is my main crypto payment gateway.

Update 12/2019 - suddenly my customer started complaining that "Merchant can't receive funds at this time.". Coinpayments not bothered to notify me via e-mail or it was not delivered to my Inbox. Reason was KYC. They want my identity card, drivers license and such (possibly due to $10,000 money transacted?). This provider is good, but i am leaving it due to KYC. I will use now cryptocurrencycheckout.com which means no KYC - money goes dirrectly to my wallet, but the process is manual, i have to check payment confirmed and mark invoice paid.