If I remember correctly Gaf ranked The Order above Halo 5 on that list of most anticipated games for 2015. I think that tells you everything you need to know about how representative Gaf is for the wider gaming market. Gaf is great because it has some really amazing members who care deeply about gaming, but if you only paid attention to this forum you'd be convinced that Shenmue 3 would outsell Madden. The PS4 subreddit's top post in the post E3 discussion thread was 'Microsoft won", but here on Gaf people are losing their minds because of the "holy trinity". Different groups value different games, so I don't think a lack of enthusiasm for Halo on this forum tells us anything except there's a lack of enthusiasm for Halo on this incredibly niche, ultra-hardcore, Japanese enamored gaming forum. We'll have to wait and see how Halo 5 sells before we can say anything more.
GAF is interested in the games that do something new in the industry and take risks, not the work horses that keep it afloat.