Anyway...
Next we have じゃないか, which I'm not overly familiar with, but I believe it's a tag question similar to "isn't it" "aren't they" etc. So 結構やるじゃないか might mean "you're pretty good, aren't you".
Question regarding じゃないか - are there any other forms that this can take? How about ではないか or じゃないですか? What about leaving off the か? Because I've seen the sentence お宅はすごく大きいじゃない which I thought meant "your house is really big, isn't it"