Like Jason, I played X4 to death when it first came out. I can't lie - I enjoyed it quite a bit. After a few dozen hours, though, I became less and less willing to put up with the game's shortcomings and it was increasingly obvious that the entire thing was rather half-baked. I, too, have shelved it until they inject some more content and personality into it. It's not even the bugs that turn me off, it's the incredibly lazy design in several key areas. The main campaign is so awful I don't even know why they bothered to release it. Coming from X:R I really miss having a story with actual characters. (And Rebirth is a very
low bar!) The tutorials are terrible. The universe feels lifeless, despite all of the NPC activity buzzing around you. It's just
boring after awhile. For me, once I make my first couple of million and have a basic economic engine going with a few ships I just lose interest. X:R kept things interesting with the main story where new sectors would open up and you'd meet new people, etc. X4 has none of that, to its detriment. I suppose if all you're after is a cold economic sim then you'll be happy, but I want more. X4 doesn't have a lot to offer beyond making money, though. Combat is a snore-fest. Exploration is basically finding a few stray crates and a ship every so often. There is no plot.
Well, Star Citizen is trying to be the end-all-be-all I guess.