You do realise Halo: Reach's marketing budget alone probably cost enough for Sony to create 2 God of War games? And your trying to compare GoW to Halo even with the fact Halo is in the most popular genre on consoles versus God of War which is in one of the least popular genres? Also Halo has been in a huge decline in quality and sales since Halo 3, what's your opinion on that?
Also even though it's exclusive to one platfrom God of War is by far the biggest franch...
What do you expect when advertisement was none existent for the game outside of the US? You shouldn't use Vgchartz numbers either, they were proven to have under-tracked the God of War series hugely.
God of War III sold 1.4 million first week and around 6 million or more lifetime (every SKU included). God of War: Ascension probably sold around 700,000 first week which is great for what it is, nobody should be disappointed for those sales, especially for a hack 'n slas...