X3: reunion is a good sandbox game, which is not for the faint of heart.
To say the scope of X3 is huge is an understatement. There are a lot of sectors and about seven races. The equipment, upgrades, weaponry, goods and ships are scattered among the races and the sectors so you are expected to do some exploration to find what you need and to find the best places for trading.
Space combat is fast and not very forgiving. It is not as simple as say freelancer and loosing your focus even for a short time will end up in disaster and will cost you a lot.
The games pace is very slow specially in the beginning and it will take time and patience to advance and reach the more interesting and rewarding parts. Another problem of the game is the interface that needs to be stream lined a lot. This is a big issue especially considering how much the game tries to accomplish. Think about it this way, in the same time you explore the world and you fight and encounter hostiles you need to keep an eye on your fleet and factories.
I started playing the game after patch 1.3 so I did not encounter technical problems that the others are complaining about and after playing about 50 hrs the game has never crashed on me(ok it crashed once when I used the to switch to the desktop).
The graphic is one of the main selling points of the game but you will need a powerful PC to enjoy it fully. I recommend an athlon 3500+ CPU and a 7800gt or X1800XL graphic card with more than 1 GB of memory. Even with these specifications in certain sectors, the game will be hardly playable. If you are, a fan of sandbox games and has a soft spot for space simulator games then X3 might be enough to justify the upgrade. You will not regret it.
You are on your own to learn the game since there is no tutorial and not even a proper manual and believe me it is worse than you might think. Imagine you need to buy a space ship and the only thing you see in the game is the spaceships name, type and price. Therefore, you cannot compare the spaceships unless you buy them both. To buy other stuff can be worse, for example even after buying a missile you will not know its strengths and weaknesses.
The bottom line is that this game is not for every one and you will need a lot of patience but if you invest in this game then you are for a great ride through the galaxy.