For me it is nowhere near as polished as WoW (which lets face it IS the main competition/comparisson) it has graphical issues, numerous UI issues, sound issues, guild issues and other personal points of annoyance which I won't go into.
Despite this I think the game is fantastic! The stories, the crew skills, the companions, the difficulty, the grouping aspect and other things are all unique and give the game an edge on all others. All the issues that I have labelled have been pretty much acknowledged by BW, which is a good start as they are not blindly claiming to be putting out a perfect product, and they have stated that these issues will all be sorted over the near future patches. Additionally the issues are annoyances rather than gamebreakers, there is nothing inherently wrong with the game (IMO) which makes it unplayable.
Lastabillity? I haven't seen endgame yet. They have gimped world pvp by instancing which is a shame. There is only 1 or 2 operations (essentially raids) and a few higher level flashpoints. However with there being 8 unique stories to the game that is a massive amount of replayabilty just there. BW have also said there will be "regular" content updates though it remains to be seen what "regular" amounts to. Personally I think the fact that it is so story driven will jar with an endgame grind and I will find it interesting to see how this pans out.
Overall its a fantastic game and well worth buying, it will be in the market for a long time to come and has potential to be a great game if developed right!