(AMZN 0.23%) posted a solid earnings report late last month. First-quarter revenue increased 17% year over year to $59.7 billion and earnings per share skyrocketed 117% to $7.09. This figure crushed analysts' average forecast for earnings per share of $4.71. 

But since Amazon has morphed into such a wide-ranging behemoth, these metrics fail to fully capture the company's performance. Here's a look at some of the metrics from Amazon's first-quarter update investors may have overlooked, including the e-commerce giant's soaring free cash flow, and its fast-growing Amazon Web Services and subscription services revenue.

A smartphone with a shopping cart icon on it

Image source: Getty Images.

1. Free cash flow

Perhaps the most impressive metric from Amazon's first-quarter update was its free cash flow, or the cold, hard cash left over after both regular operations and capital expenditures are taken care of. Amazon's trailing-12-month free cash flow ending March 31, 2018 was $23 billion, up from $7.3 billion in the year-ago period.

2. Online stores revenue

Amazon's first-quarter online stores revenue, or revenue primarily from sales of e-commerce products and digital media sold on a transactional basis (as opposed to a subscription), increased 10% year over year in constant currency. This is a deceleration from constant-currency year-over-year growth of 13% in online stores revenue in Q4.

With online stores sales accounting for half of Amazon's revenue, this deceleration is worth noting. Continued deceleration in the coming quarters could be a concern.

3. Third-party seller services revenue

Fortunately, Amazon has some other fast-growing segments helping make up for slowing online stores revenue growth. Third-party seller services revenue, for instance, increased 20% year over year in constant currency and accounted for nearly a fifth of total revenue.

4. AWS revenue growth

In addition, Amazon Web Services (AWS) revenue continues to soar. The cloud-computing segment's revenue rose 41% year over year in constant currency, representing 13% of total revenue. This segment's rapid growth is important because AWS boasts a lucrative trailing-12-month operating margin of 29.1% -- much higher than Amazon's consolidated trailing-12-month operating margin of 6.2%.

5. Subscription services revenue growth

Lastly, consider Amazon's soaring subscription services revenue, or revenue from Prime memberships and audiobook, digital video, e-book, digital music, and third-party and non-AWS subscription services. Subscription services revenue during the quarter increased 40% year over year in constant currency -- an acceleration from 25% constant-currency growth in Q4.

As these metrics point out, Amazon's business growth is coming from various sources. This is important because it means investors aren't totally dependent on one business, such as e-commerce. Subscription services, AWS, third-party seller services, and online stores revenue are all key drivers for Amazon's growth. And this broad-based approach is generating significant value for shareholders, sending free cash flow through the roof.