This one's a bit formulaic, truth be told -- although the last scene is sweet.
The Merlin Wiki has a summary here.
Merlin does something rash because he believes it will help a magical being, earning a scolding from Gaius. Merlin and Arthur then go on a quest to undo the damage. Like I said, this is standard fare for Merlin. The building blocks for this episode have been used in many other episodes -- and unfortunately, they've often been used more creatively before now. I've seen far more compelling quests -- and Merlin has, in the past, suffered much stiffer penalties for his adolescent impulsivity and over-confidence. Indeed, just last week, we saw a grand plan of Merlin's backfire in the most spectacular way possible. And now we're moving on without really focusing on the repercussions? Seems odd to me -- like this episode has been tragically misplaced.
But hey -- the birth of Aithusa does manage to recapture some of the "sense of wonder" that is missing in the rest of the episode. Consequently, I wouldn't call this outing a total loss.
Sadly, this script is pretty boring. I feel like it should've been harder for Merlin to reach the dragon egg.
The performances are also strictly average. Nothing stands out.