Great episode, and as for the coffin that is protected with a spell: My guess would be that Klaus' mother is inside ;) I think he doesn't want her out. Think she could kill him easily as she is the first witch. And in previous episodes we already have seen that the first witch doesn't like Klaus ver much ;)
Let me start by covering a few things raised by other people. Firstly, the show has not ignored a plot hole about the daggers killing the vampire who uses them. It kills normal vampires but it does not kill Klaus, it would be a bit silly if the dagger being plunged into his heart could not kill/incapacitate him but him using it on someone else could..., now i know in a previous episode Rebecca stabbed klaus with a dagger and she didn't die, two possible explanations, firstly, it didn't affect her because it doesn't work on klaus and therefore the other part of the dagger doesn't work either or the dagger does kill the vampire who uses it but that rule not only doesn't apply to klaus but does not apply to all the originals.
now, Jeremy leaving? is it forever or just a while, it all depends on the reasons behind it, having not read the books i don't know but there are 3 options, he is gone for good because the character wasn't adding enough to the show, he is gone for a while and will be brought back as part of a plot twist, or he was written out permanently or temporarily at the actor's request for some reason. I hope he comes back.
Now, to my main point, the coffin which will not open. The idea seems to be that whatever is inside it is the key to defeating Klaus, or that seems to be the inference. Now, taking a few things into account, the fact that Klaus,presumably, has had the coffin sealed with magic, secondly, the dreams bonnie had where she sees "klaus" in a coffin with a necklace similiar to elena's, i am not 100% sure it is a different one but i think it is. Here is my wild prediction.
Klaus is a twin and that his brother is in that coffin, i know it is a crazy idea but it just popped into my head,it would explain how the contents of the coffin could be used against klaus because his twin would also be a hybrid and therefore would be as strong as him.
Secondly, it would raise a few interesting questions, for example who killed their mother? klaus or the other one. also, we know that klaus hasn't always been a bad guy, in the flashbacks to when they were human he seemed almost normal, so the questions would be which "klaus", obviously they are not both called klaus, but which one did various things throughout history and which did they swap places at any time.
Now, the most likely reality is that next week they will open the coffin and I will be proved wrong and all this typing will have been for nothing.
one other theory that popped into my head is that the coffin contains a witch, ayana perhaps, but that begs the questions why would klaus keep it.
Yes, Klaus' revenge wasn't that elaborate, but I'm pretty sure that's normal, he doesn't want to hurt his family either, so I'm guessing that's why he takes less risks. Stefan... I'm not sure about him, some people picture him as a new Damon, but I could not agree less with that. I'm uncertain what he wants and how much he feels now. His humanity is not completely restored, I believe.
I thought Jeremy's plan to leave town was a very sensible reaction (of course, Klaus would find them, but it seemed like a human, normal reaction). And although I feel kinda sad they sent Jeremy away, I think it was a very realistic option. Besides, what storyline was there left for him now? Bonnie dumped him and he was back to being the grumpy rebellious teenager. I do hope to see him return some day. Maybe with a vampire on his arm :p
Anyhow... very nice and touching episode. I was suprised that Klaus stabbed his sister again, but it did make sense ... somewhere. I though this was a very ambiguous, thoughtful episode. I really liked it.
And don't get me started about the ending: fi-na-lly. Of course Stefan will probably redeem himself and all that shit, but come on, even Stelenafans must have found that a great moment. And typical Damon, it shows how he wrestles with being 'human' and just going for what he wants. Sometimes you just do the latter, no matter what..