For a free tool, StatCounter is one of the most well known simple site trackers. Very easy to set up and use. Great to have an independent source aside from Google Analytics to give you stats on Keyword Analysis, entry and exit pages, search engine stats, referral info and details about your visitor. Also, their 'Visitor Paths' feature is very useful to see where users travel on your website pages.
I really like the configurable summary stats. Great to get an overview of your site performance.
No real-time stat dashboard like Google Analytics has, but it isn't a deal breaker. For a free service, StatCounter is very feature rich and provides you what you need without the bloat like other stat services. It doesn't offer HTTPS secure tracking for free.
As a free service, it is worth checking out
Tracking stats is fairly straight forward, you see if your site is growing in visitors or not. However, StatCounter's 'visitor paths' feature allows you to take your stats further into actionable steps to improve my website. I was able to look at the visitor paths and see where potential customers were getting stuck in the sales process and make improvements to those web pages.