I've played Factorio on and off for over 5 years now, joining the community about half way through it's long development. I can safely say that it's been an absolute pleasure to watch this game grow and evolve to what it is today. Now on to the nitty-gritty:

Factorio is one of those games whereby there is no "right" way to play. It's ultimately sandbox, and ultimately YOUR factory. There is indeed elements of efficiency, supply, demand, production, and loads of maths and flowcharts you could potentially employ to make your factory the "best" at least in terms of efficiency...but it's not required...at all.

There is indeed a clear early-game, mid-game, and end-game, it often starts off very slow but will vastly pick up the pace. At that point, you can really set up YOUR own pace and again, play how YOU want to. What's more? The game doesn't "end" in the traditional sense in the end-game, you can keep playing and making and producing more and more, or perhaps start again but this time throw in some of the numerous modifications that are avaible on the website to spice up YOUR Factorio experience.

Like most games these days; Factorio is much more fun with friends, the multiplayer is currently a bit clunky though it is subject to vast improvement, especially considering the potential for Steam Integration. Be wary though, when playing with others they're will inevitably be a clash of opinions, your friend(s) may want to build something their way, when you would like to build it another way. As cliche as it may sound, the following moral applies here: "There is no "I" in team". Logically work out your differences and teach each other differing ways to accomplish the same thing. Then come to a consensus and continue building a GROUP factory. Playing with friends will ultimately help much more than it will hinder.

Finally, I will say that Factorio is one of the absolute best games I've ever had the honor of playing. I look forward to seeing where it goes and what the future will bring, and I encourage you all to join me in the journey.

"Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning."
~Winston Churchill

~TL;DR~
Why are you reading long reviews that may or may not tell you anything? Buy it, you won't regret it.

Edit:

The game has now fully released, and my review has not, and will never change. Buy the game...and grow your factory.