Looking over the archive, it looks to me as though each act of Homestuck has it's own character, except 2 and 3 are the same:
Act 1 is about John, and towards the end Rose, messing about in their Houses.
In Act 2, the story seems to develop an overarching, fantastic, dramatic plot about SBurb.
Act 3 just continues what was in Act 2.
Act 4 ups the drama more by making the high stakes of SBurb clearer. Also in Act 4, the kids' session begins to go wrong, extending the high fantasy plot beyond "Some people play SBurb, which means ...".
Act 5 brings the trolls to importance, gets non-chronological, and introduces "the mythology beyond the game", as Rose calls it.
Act 6 brings guardianswap, and I'm guessing it will do or has done more that will be more obvious in hindsight.
So. Why are acts 2 and 3 seperate? Is there a difference?