Tekkit provides a short burst of fun. A new, fresh Minecraft experience that amazes for a few days and then quickly frustrates. It requires one to be experienced with vanilla MC and somewhat tired of it. If it catches you in that period of time after you've had enough of vanilla for a while, it's priceless. But I don't see it ever captivating anyone but the most dedicated group of players for more than a week or so.
I am sure Tekkit (or FTB actually, since it's the same mods, only better) can make a return some time. Right now Vanilla just sounds much better though.