X has its faults, but it's does so many things that are fun:

• You fly using an actual joystick (you can use keyboard and mouse, or gamepad, or whatever, but these days a space flying game with a joystick is pretty rare)
• You get to fly everything from tiny scout ships to massive destroyers
• It's a sandbox game: like just going out and killing baddies? Plenty to kill. Like becoming a pirate and killing good guys? Go for it. Prefer staying out of combat and instead moving wares from station to station, making profits? Yup, you can do that too. Prefer cutting out the middleman and building your own stations? Yup, it has that.
• There are dozens of ships, each with subtypes. Each of the races has its own scout ship, its own interceptor, its own heavy fighter, its own carrier, its own military transport, and so on. Each ship looks unique, and each race has its own style.
• Most ships can be bought, but some ships can't be bought, to acquire them you have to capture them, giving a unique reward for a fun challenge
• There are many different types of energy and slug-throwing weapons, and many different types of missiles, and you can pick the ones that suit your play style

There are a few downsides though

• The initial learning curve (first hour or so) is incredibly steep
• The main plot is somewhat weak, the missions often feel almost like MMO grinding quests
• The autopilot / navigation AI is terrible, and sometimes kills you or your ships by just driving into things, or driving through an incredibly dangerous sector instead of taking a safe route
• Weapons are the only real ship customization you can do on your own. You can't tweak the engine you use, the shield types, the power plants, or anything like that.

To me, the game feels a lot like the other Spreadsheets In Space game, Eve Online, but with out the "online" part, with less customization of ships, but with dogfighting in space.