EQ II is going strong, better than it used to be. It's nowhere as popular as WoW though, and I believe that even guildwars has more accounts, but it's definitely not dying down!
EQ II is more group oriented than other games, but there is plenty to do on your own too. I have never grouped much myself, but I haven't heard many complaints about people finding one.
The community in EQ II is great, pretty mature I'ld say.
And there are guilds in EQ II (Foundation on Najena for instance!), which are very comparable to linkshells in FFXI. There are the larger raid guilds, usually with some requirements regarding lvl and playtime, and the smaller family-type guilds (such as Foundation on Najena!). Lots of guilds vary in between the two types.
All in all, the game is definitely worth trying out. And quite cheap to purchase too, if you get the retail (not the digital version!) version of the latest expansion Echoes of Faydwer, you get the original game and all three expansions at once.