actually they changed that instance design as it wasn't doing what it was supposed to be doing, there were other ways of doing it

I've played both games and prefer LOTRO, but even then I have to admit that if you like raiding, stick with WoW. LOTRO's end game content is either 1 main fight a week(watcher) or an upcoming Rift-like dungeon with multiple mobs(once a week also, 1 to 2 days to finish). So if you're used to logging in WoW every single night and really like raiding every moment, I wouldn't touch LOTRO.

If you like to do other things(like housing, collecting trophies, tradeskilling, etc etc) than raiding, then try LOTRO, its much more diverse in gameplay.