I've had some difficulty with the storyline of this DLC and how to properly fit it into ME2's plot. The reasons are due to a few things that I don't think are properly cleared up:
1) Kenson says "the Reapers will arrive in the system regardless, but without the relay it will take months or even years for them to travel anywhere else". So the countdown is, I assume, a countdown to their arrival via their own basic FTL travelling means, just like any starship is capable of FTL travel outside of Mass Relays, right? But with the slamming of the asteroid into the relay it is still heavily implied that they will arrive -via- the relay and that by destroying it we gave ourselves a few months more. So which is it? It seems fairly ambiguous to me.
2) If the Reapers were planning to invade via a secondary invasion point, what does that say about the attempts of Sovereign in ME1 to open up the Citadel as a central relay? Even if they only started moving to the Alpha Relay -after- the failure of Sovereign at the Citadel, you have to wonder why they didn't just default to the Alpha Relay invasion as their standard plan? Because it apparently takes them only two years to get there from dark space, and they can do so in complete secrecy because even though Object Rho may still have been found, noone would've had a clue as to what it would've signified if it wasn't for Sovereign earlier.
3) When is the correct time to play the content of Arrival with the earlier two points in mind? Before or after the suicide mission? At which point in time does it make more sense? If you play it before then you can justify the collector plot (which I expand on below) as being a failsafe plan for backup Reaping should their alpha relay invasion also be foiled, but then the final shot of the game fails because it clearly shows the Reapers still approaching the galaxy, whereas, judging by Kenson's words earlier, they should already be in it even if not anywhere near the core. If you play it after the suicide mission, then the significance of what you accomplished with the collectors gets sort of devalued.
These are basically my three main challenges with the plot here. The thing is that I love Mass Effect, and while you guys may know that I tend to rag on the Conduit plot, I've come to accept it as Saren and Sovereign just wanting to find a way to ambush the Citadel forces as well as they possibly could, even though it may not have been necessary to risk what they did. The problem I see with Arrival is that it in part invalidates the entire plotline of ME1, when the Conduit plot could've been stronger from the outset, and it invalidates what the Collectors were doing in ME2, since why would Harbinger have the collectors scrounge up bits of human DNA at a time (a colony every few weeks isn't exactly efficient reaping by murderous AI standards) when he knew full well the Reapers were about to invade anyway?
Now I grant that the latter invalidation may still be rectified in ME3 and that there are very justifiable reasons for the Reapers to plan things as they did, but I'm left to work with what I have.
All in all I just find Arrival a very annoying piece of additional story and it bothers me because I love Mass Effect as a series and I want to keep loving it and not be annoyed by these stupid inconsistencies. What have you guys made of all this? Is there stuff I'm just not seeing?