If you've played the rest of the X series, you would know that what you see on screen doesn't really vehiculate the depth and excitement that the gameplay is based off. For one, I am really stoked to see a Space Simulation that has graphics that don't border on the atrocious or that goes for the cheap arcade shtick that dumbs down the complexity of space flight.
In recent years Space games have been completely left behind for either extremely shallow mission-based games or 4X games that play like a really boring chess game intersected by cinematic battles you don't even pilot in.
This is a HUGE breath of fresh air for a genre that has many hardcore followers that have been forced to survive off X3 for what it seems like forever now.
Star Citizen should pretty much completely outclass it. For one thing, from what I hear about the X series it is way more needlessly complicated that it should be. In that, it takes forever just to get anywhere, there are a ton of functions and commands that you need to know, and you don't actually get to spend much time in combat.
In contrast there is Freespace 2, one of the greatest space sims ever. 80-90% of the time you spend in that game will be spent in breakneck dogfights or coordinating an attack with your bombers to take out a capital ship. On top of that, Freespace 2 has great graphics mods.
As a lifelong Rogue Squadron fan, I jumped head in into Freespace 2 after hearing it is only 6$ on GOG and I spent over a 100 hours in the game so far. I was previously eyeing Tie Fighter, but Freespace 2 has modern graphics on top of full kb+m support and you can easily acquire it.
Star Citizen should pretty much completely outclass it.
Seeing as Star Citizen has many times the budget, many times more people working on it and it won't be coming out for at least a couple of years - If not longer as they keep promising new features. Personally, I suspect that Star Citizen will in many ways be too simplistic for the type of game it is - Like Freelancer - Kept simple to appease the maximum number of people who are funding it.. Whilst the X series is overly difficult for most people to get into, should you manage it, it is intensely rewarding.
Still, I'm not too fussed, I plan on enjoying both games (And Elite: Dangerous) thoroughly.