I live in Europe, in a country without Amazon, however I often travel to the UK so I've had a few opportunities to use their services.
My experiences have been very mixed. The website, in my opinion, is a mess. It's extremely hard to find things unless you know specifically what brand and model you're looking for. Even then you might find that someone decided to sell that item for an inflated price.
Generally when you're browsing for something you want but haven't decided on an exact brand and model yet then discoverability is terrible and listings become irrelevant pretty soon after scrolling down. Even trying to find a gaming laptop for a friend to buy is a useless endeavour.
Shipping within the UK also seems to be terribly implemented: more often than not your packages are going to get lost, misdelivered, forcing you to fight for the goods you've already paid for and potentially get them way too late if you want them by a specific date. In August, when I was visiting, they managed to misdeliver 4 items I ordered and it's always Amazon's delivery team that messes up.
The only reason I really like them is the book market and second-hand book market. It's great to be able to buy so many books at such great prices.
In my own country, however, e-retail seems way more sophisticated: discovery, delivery and reliability are king. They optimise the listings for you to be able to browse and find things efficiently, to discover stuff you want quickly. And it's very rare for the shipping to take more than 1 day, unless there's a seasonal event like Christmas/New Year's. So I buy with confidence and I browse knowing that I'll usually find what I'm looking for. When it comes to buying from Amazon while I'm visiting the UK - I always expect issues. And they always happen.