While for the most part there isn't a major issue when actually viewing Netflix, it does have some problems when it comes to the level of quality it can provide.
While it does profess to offer 1080p HD, this isn't always available - a number of web browsers, including Chrome and Firefox, can only play Netflix at 720p, which is worse than what you get on Internet Explorer, shockingly.
That's not the only thing stopping you from getting a good viewing experience though. Netflix offers four different settings for quality: Low, Medium, High, and Auto, which vary between quality and data usage (the higher the quality, the higher the usage). Auto offers the option of it fluctuating depending on what your current speed is, but that means you're more likely to get a drop in quality too.
There is another problem with Netflix when it comes to HD as well. While it does now offer Ultra HD, or 4k, as its most premium product, it's very basic one -£5.99 per month - is SD only, and it's the mid-tier (£7.49p/m) package that includes HD. Amazon Prime Video has many flaws, but when they're offering 4k as standard, Netflix needs to up their game.