They were basically just trying to do what they did in Season 2, since they had a battle coming up. The entire season of the Night's Watch arc has been one long delaying tactic so they could put the battle for the Wall in a big single-location penultimate episode and recapture what was in some ways the previous high point (other events got talked about more, but that was due to the extreme tragedy and/or shock value) of the show.

And they even added a bunch of stuff that was not in the books to try and hit those same notes, like the ranking leader, already despised for his part in Ned's murder, letting someone else command the battle and eventually sneaking to preserve his own hide, or the boy saving the main character with a last minute attack from behind.

I wonder if next season, Jon & Edd will be eagerly pressing Ollie for the tale of his exploits in Mole's Town after they send him to the brothel out of gratitude?

It wasn't a bad episode, and the action was probably the best they've done on the show so far, especially on a large scale (it was pretty obvious that there were not large armies behind the handful of guys you actually saw fighting in Blackwater), but dramatically, the characters even admitted at the end that nothing had changed as a result of their efforts, whereas Blackwater was a complete reversal of fortunes that set up the status quo for the next season. This? Not so much. In the book, having at least three different battle scenes at the wall, with the increasing attrition of each one wearing down Jon & the brothers, you could see where he would make the decision he makes at the end of this one. Ironically too, I think the circumstances under which Jon heads out for his suicidal assassination attempt in the book might have better fit with the situation on the show. As a result of the great big battle, with Jon leading, slaying the Magnar and capturing Tormund, he'd be a major obstacle Slynt would want out of the way, giving him an additional political motivation to send Jon to his death.

But, rather than spend all those extraneous episodes with Gilly or the brothers talking a bunch, or a made-up raid on Crasters, or Ygritte being a bitch while she and her companions wandered the Gift, if they had just had the series of smaller battles, maybe the hopelessness of the situation, and paucity of their resources would have been better conveyed. There was really no justification for doing it this way, unless the showrunners felt some sort of compelling need to recreate the previous high water mark for epic battles on the show.