I don't mind the map re-use. We can't realistically expect them to create all new maps all the time for these things. That would be far too much development expense. If they did that they'd have to charge for them as DLC like MW3's "let's release one specops mission with each multiplayer map pack". Screw that.
Landed on exactly 500,000/500,000gs with exactly 18500 achievements and exactly 500 games. All 100% including DLC. Was going hard the first half of January to reach that goal! Finished it on 1-19-2016. Final achievement: Completion Serenity in Nero.