Wow, I really did not see this one coming. In the comic Dale dies much later and has a very odd relationship with Amy and Andrea. He ends up having such a cool death that I could not imagine them not wanting to use that in the show.
Instead they decided to kill him off just as he was making his point to the group about why they cannot murder Randall. Fortunately, his death will have more repercussions than just Randall. Earlier, Carl was throwing rocks at a zombie stuck in the mud. This pissed it off and it pulled free and almost ate Carl (who then lost his pistol).
Carl blames himself, which could lead to two things: he tries to hide it and be more like his father, which leads him down a very dark path, or he could tell his dad about it and feel like his family and the group hate him, which leads him down a very dark path.
Also, we get to see Daryl become a more prominent member of the group. He has been a little bit mopey after finding out that Sophia was a zombie inside the barn. I believe that he will take up Dale's anti-Shane stance (and may actually have the physicality to stand up to him). I also believe that Andrea will want to preserve Dale's memory and become the moral center of the group.
How will this affect Rick? I think he will blame himself and begin to second guess his decisions. He will believe that Dale died because he (Rick) made a decision to kill Randall, which caused Dale to take that fateful walk. If only he had listened to Dale and given Randall more time...
Anyways, it should be an exciting rest of the season.