I think it's totally ok, to use some of the same walkers and stuff. But it did annoy me, that the couple from the room in "No Time Left", that had killed itself on the bed, now lies in the group that was killed on the river. The man is looked at by Nick. And the woman lies on the other side in a somewhat awkward position. (to me it looked like they took her body and just put it there in the same position as on the bed, but flipped over)
Was I the only one to notice? Is that supposed to be some sort of easter-egg?
Anyway I didn't like it.
update: So, just to show what I mean, i made some screenshots
The Couple in Season 1:
The Woman in Season 2:
The Man in Season 2: