What distinguishes one Linux distribution from another?
- The package manager and available packages
- The default software choices and configs
- Technical documentation
The package manager specifically allows for third parties to put together their own packages in the form of AURs. So if something isn't officially available... chances are it is available as an AUR.
As far as defaults go... you pretty much need to install everything you want. That's the beauty of it. You don't get saddled with a bunch of stuff you don't need.
The documentation available on the Arch Linux site is fantastic. This is a huge help. Before I installed Arch Linux I had read that the documentation alone was a huge plus in favor. And after going through the install process I can say it is a very nice thing indeed.
Some folks maintain that Arch Linux is difficult to run. I haven't found that to be true. In my one or two days with it... I already have pretty much everything working that I would typically set up on a Linux machine. And honestly it was easier than with many distributions that are oriented toward beginners.
One area where Arch Linux differs from many other distributions is how new releases are done. Arch Linux uses a rolling release system. So there actually are no new releases. Updated packages are made available to the distribution when they become available and are not typically bundled with other packages in the form of a scheduled "release".
This means you are always as up-to-date as you want to be. One command will update all of your installed packages in one fell swoop. Of course there is a certain risk of breakage. Maybe a little more than with distributions that used the concept of scheduled releases. The term "bleeding edge" might be somewhat appropriate here.