Well plenty of ppl still play this game most on this site would properly complain about all the good ones leaving which is utter nonsense im still here!
Anyway getting expansions are a if, if you enjoy the game personally my fave expansion is factions its got a rich storyline and brings in the fun of choosing between kurzick and luxon into the game. If i was you get Eye of the north last but feel free to skip Nightfall its the weakest of all the games.in my opinion it does however introduce heros and PvE only skills that are very useful. However story wise and title mission wise its my least favorite Palwa Joko (spell check) kicks ass however

Prop the first game is the biggest baddest of the bunch also the hardest for example reaching the maximum level takes..... a large amount of time to achieve, in factions you are lvl 20 in about 2 days.
As for other advice when you get eye of the north Do not use ursan blessing its recently been nurfed not what it once was and its just plain cheating at the game and if you hang around on this site the amount of times you will be called a fag is ...... interesting.
secondly get yourself a good guild one that helps and friendly ive been in the same one for ages now the game is based upon teaming to beat the environment get a good group of peeps around you and it will be worth it
As for is it worth it to get back into it.... its more than worth it guild wars is still a great game despite the people complaining that it has changed of late. The Sequal guild wars 2 quite possibly the most original name ever! will be out in ...late 2009 i believe. Believe me when i say there is plenty to do in Guild Wars and I personally am afraid of Guild wars 2 being resealed before i 'Finish up' title wise.
Good luck in Guild Wars!