Very well... I'm going into Excel to plot some graphs.
I'll have a scale from 0-100% in values of interest and mark up arbitrary points in time labeled by events. Either new post or editing this one when I'm done.

Well... For my ominous talk my graph sure is quite simple. I'll wall of text the explanations here as opposed to trying to work them on the graph and make it even longer.
It does not fit the width of the board so:
http://i.imgur.com/AAdoQ.pngFirst, it's really linear, instead of multifaceted. That's because of one simple reason: I never spent time in the ARG because of one aspect or another. It was the whole package, with all the story lines even if I didn't actively participated in them, or nothing at all. So the points I make note of are only the Major breakpoints. Of course, I had a very heavy spike of lack of interest during the DQ Echo's event where I almost ragequit and ended up sending a threat email to Morgan (sorry Dana!), but that was quickly fixed and not lasting so not worthy of a point in the graph.
Well, on to the points:
- ARG Discovery: I'm familiar with the concept. Always wanted to play one. The moment I found that one was going on and I might just be able to join? Awesome.
- AJ Channel: Good. But, lacking in content... Ok, I'm watching the videos... But there are only a few videos.. Just waiting, purely waiting and nothing else.
- Downtime 1: I absolutely forgot about the ARG. There were no updates or I simply didn't remember to look for them. I let it fall to the background and went on with my normal day-to-day.
- Megathread: I had never used the TvTropes forum. Even though I was a known troper back then, it just seemed lacking somehow, and I didn't join.
- Downtime 2: Again, lack of flashy things. I wasn't in on the talks going on in the megathread, nothing to do. I just forgot about it. Then one day I saw that youtube had updated.
- Forum Update: So I caught up on the videos, Joe was running and there was a forum now. Well. I can lurk there, see if there's anything interesting. Lurk I say. I only joined to watch and nothing else!
- Start of Interaction: I simply started talking on the forums. That was bump to my morale. It made me stick around.
- Character discovery: Oh god the anxiety to figure out who was the next character to discover! It was exciting, very much so. It was also when I got the rush of finding the blogs and felt awesome for actually contributing!
- Echoes and Layar: That was disappointing. I expected to be unable to do anything being in Brazil. Victim of my own stereotypes, I say. But I had the feeling that I was actually contributing and then suddenly it hit: No, your country is not on the game for this. The hit wasn't so big though. The playerbase was accepting of it. I looked up to Dryu from the moment I joined for his work on the metaverse and all around awesomeness and then he was cut off from Layar as well... I felt I was not alone and that I could still help out, a bit down for it but still good to go.
- Writing Assignments: Ok, now that's awesome! Admittedly I didn't write a lot, only one Anansi Fic, Don's Fic and my single C!Fic. But still, that premise by itself boosted my humor a lot.
- The Cabal starts getting real screen time: Yes, I loved Erik and Morgan's characters. We didn't get much interaction with Juan or Moriarty, but still they were an awesome and interesting team. But I got a nagging feeling that I was in for trouble soon. And I was right.
- Broken Base & Secrecy: That was beyond tense. I wanted to quit more often than I wanted to log in. Really I hated everything about that idea. I was nearly breaking by then.
- Tram Wreck: Then I broke. Simple as that, I had no motivation whatsoever to stay here anymore. I didn't want to be here anymore. I told in my post explaining why I got so down that I don't know why I came back... Well, I don't, but I'm glad I did, because...
- Unified Ending: That was awesome. It was everything I wanted to happen, a single unity, everyone working together. It overshadowed everything I had thought in regards to leaving. Made all this time worth it.
- Post-Mortem: Then you come along and start being awesome and talking about everything with us openly, it might seem from the 120 that I'm liking this more than the ARG itself, but that's not what I'm trying to say (the two are incomparable due to being different in nature anyway), what I want to say by that is simple: For all my opinion is worth, everything you did and this whole package is one of the best experiences I've ever had. And I'm proud to be a part of it!
I can do something similar for each arc, a review of sorts about each character's plotline... What I though were the good things and the bad things of each one. If you do want that sort of thing from us. But as far as engagement goes, I can only give you the view of the ARG as a whole, because that's the way I view it myself.