It's a robust game without a robust community, but it's still a robust game. The problem is that the leveling system - required to unlock all the fun gadgets, guns, and customization options - calls for a good bit of playtime to get going, and you'll usually find but one or two populated servers at any moment. I want to recommend it as an immediate buy simply because the core game should be experienced while it's still alive, but it's worth knowing what you're getting into.
The SP can be tough going due to bot stupidity, but it's playable. The character creator is famously deep. And while this probably doesn't amount to much of an achievement, it has the best world and character design of any multiplayer shooter since Team Fortress 2.