I opened my Amazon card in March of 2014. It was also upgraded when they tied it to the Prime benefit. I use it every month - sometimes just a small purchase or two, sometimes a lot more, lol. Very heavy use around holidays! I have never had a bad experience or any issues. The only small quibble I have is that I seemed to be nickled and dime'd with CLI, all were initiated by me. Currently at 10k limit, have been perched here for awhile, and I'm fine with that. As for some comp points - I pif 99% of the time unless, sparingly, I use one of their financing offers. I always ask for any CLI on the phone, not via chat. All of my fico scores are mid-800's, although when I opened this account I believe I was in the low to mid-700s. I'm not afraid of adverse action on any of my cards, I figure I'll deal with it if it ever comes up. No living in fear. 
I've had mine a little over 5 years. My only real issue was that the credit line grew very slowly before I found this forum and that once you reach a certain limit, the LUV button will always deny you so you do have to call Credit Solutions. Honestly, their options for being able to assign how your payments are allocated to promotional and new purchases is top-notch and I the Promotional Purchases tab clearly shows you everything you have at 0%, the original balance, the current balance, the amount of interest that has accrued to date and the date that the promo expires where you would actually be charged that interest. I have had zero problems with payments. I run about $9-12,000 a year through mine and have never had any problems with how the payments get applied, either.
Other than for a CLI, the only time I have needed to contact customer service was when I had an item show up on my account that I didn't purchase. Someone must have entered the wrong account number on their Amazon account because the card itself has never left the house so no chance of it being skimmed or anything, and it was for a modestly priced item of clothing so doubtful that it was deliberate fraud. They were very helpful, issued me a new account number right on the spot and gave it to me so that I would be able to use my account before the new card arrived (I order from Amazon 1-3 times a week) and were quick to credit me for the transaction that wasn't mine.
Completely agree that the majority of the bad reviews would be due to "user error." Don't bounce payments, don't miss payments, don't run all of your other credit cards up to 90%, don't open 25 new Synchrony-backed credit cards in a week, etc... and you will be fine. Don't expect Amex Platinum/Centurion or Chase CSP/CSR levels of service, but their customer service is certainly no worse than a majority of lenders. The 5% statement credits are great, and the real advantage this has over the Chase card is the promotional financing - can't beat 0% APR for 6-24 months if you need to make a large purchase.
Never really had any bad experiences and the times i didnt receive an item, Amazon itself sent me a new one super fas and one time credited me back for a dvd i baught, they said was returned by mail, i received it though, and allowed me to keep the dvd and credit. If one pays when one is supposed to should have no problems with cld but being part of the Sync family of cards, can be subject to shutdown if you receive a blue envelope for income verification and tefuse to comply. Thats one possible reason some cant login to pay the account. Overall, one of tge best store cards around if used correctly
I was just thinking- reading the reviews out in cyberspace from the general populace was like asking a Kindergarten class their thoughts on the matter. It's nice to have a bunch of PhD students to consult
Count me as another who hasn't had any problems after two and a half years. I've gotten a lot of use out of mine both for the 5% back and the financing. There was one time I paid a couple dollars of interest because of the way my payment was allocated, but they give you options to change that. I did and since then I haven't paid any interest or had any trouble with the financing. I had the same concern as you after reading the reviews, but I've come to realize that probably a majority of those writing negative reviews of things on the internet are just a bit incompetent.
