We assist merchants who are using Shopify Plus both online and in physical retail stores. All but one of our employees directly interacts with Shopify on a daily basis; about half of those employees are developing or supporting Shopify Plus merchants in some way.
Scales incredibly well. Forget about hardware concerns, load balancing, downtime, etc. and focus on eCommerce. We've seen merchants go from a few thousand dollars per month to having million dollar days, all on Shopify without having to worry about performance or scaling systems.
Great new features consistently being added, ahead of the curve on almost everything
Solid API to build on and work with, a few annoying quirks here and there for super complex use cases but overall very well documented and works well
Most Merchant Success Managers are good and genuinely want to be helpful
A fantastic user interface, very logical and easy to use
Tons and tons and tons of out of the box integrations. Easily the best integration marketplace of the e-commerce platforms. There's an app for that.
Some very enterprise features are missing. Vaulted credit cards only work via the Shopify Pay (different than Shopify Payments) and aren't saved to customer accounts. Probably in part because of this, recurring subscriptions are not possible without using third party apps which is super annoying and those third-party apps hijack the native Shopify checkout so that they can take you to their checkout where they can actually save the cards. Shopify does not seem motivated to change this anytime soon either.
Some merchants are frustrated that they have to use apps for functionality that they would otherwise consider essential such as wishlists. Shopify would argue that they are best as a platform and would rather empower apps as that results in an even better user experience since there are options for different apps, app developers are more incentivized to go deeper and build better, etc.. In most cases I believe this works well.
For merchants doing 500k/mo or more, the additional functionality afforded by Shopify Plus is definitely worthwhile. Negotiated credit card fees, increased API limits for customization, a dedicated MSM and priority support contacts, ability to have more than 15 staff, prioritization by Shopify Partners/experts, all add to Shopify Plus's solid value proposition.
Shopify Plus is way ahead of the pack in terms of features, automated and worry free maintenance / security / scaling / infrastructure, customer support, and speed. We've been building eCommerce sites for over a decade and it seems almost every positive trend in eCommerce is set by Shopify. They also attract the best talent in the industry.
Shopify is a solid foundation for an eCommerce company and I'm confident it will be the market leader for a long time to come.
I would recommend Shopify Plus to any merchant doing at least 500k/mo and doesn't primarily do subscription products. High volume merchants who run complex subscriptions may be better off on an eCommerce platform that doesn't rely on third-party subscription apps that can't even use Shopify's native checkout. Merchants doing under 500k are probably fine with one of Shopify's normal plans rather than Plus.