I have played the Arrival DLC and I thought it was all right.
But it felt like that they were trying to put as much action as they can into an hour or so, which to me felt like that ME2 lost some of its gameplay element, And also the timer for when the Reapers invade felt like I had to rush though the DLC just to complete it.
But it did add some fresh twists to the gameplay like the sneaking section and that you are on your own for more or less the entire mission.
But that just me, I want to what see you thought about the DLC