Not to steal the thread, but yes, Castellans are worth every point I found...with one BIG warning. You can't get them to At the Double. They have decent move, but with the rest of my army either calling At the Double or else using Wings of Terror I found myself leaving my Castellans behind in many games. So it would be several turns before they got into the mix.
Once they were there though, they scared about every player I faced and with good reason. Almost every force in the game has lower Courage than their Defense and in cases like Dwarves it's a big difference. Especially if my Nazgul hit an enemy with a -1 Courage spell (and even better if another Darkness caster did the same right after
). The Castellans have R2 and a high Defense and are hard to take out, and are Indomitable on top of that. But with Spirit Grasp and a decent Strength against a relatively low Courage you can really cut thru the ranks. To top it off, Spirit Walk is amazing for tactical situations. Pass right thru other Formations or obstacles to get to the ones you want to attack and hit them from the rear or flank to lessen their retaliation.
They won't win a game for you, but if you can get them where you need them in time (damn Stand Alone rule!) they are a better force than two Trolls in my opinion (and for half the cost).