Due to the awful condition of Irish internet connectivity, I finally got online around 2009/10. As a result, most of my memories come from Halo 3 campaign marathons and Reach customs.
I must have wasted hours exploring every inch of the campaign levels; found some pretty neat things that I thought were really cool at the time. As for Reach, I made some great friends during the 2 years before Halo 4.
Although a standout moment is split screening TGFW with my brother. I ended up getting the half broken controller. I couldn't run forward without it stopping and starting, so I had to run around the map backwards into every objective.
Halo 5 is fantastic. Sure it had launch problems, mainly due to lack of forge and playlists. But 343 have done a great job with the free updates. In my opinion, one year on, Halo 5 is the best fps experience on Xbox One.