Just finished my new run of the series. I played 1-4, Reach and ODST at release but never bothered with 5 or replaying them. As much as people seem to dislike Halo 5 campaign-wise I actually enjoyed it a lot, it could have used a bit more fleshing out of the newer characters to the games but I enjoyed it nonetheless.
Reach is still my favourite, they did a marvellous job of conveying the sheer hopelessness of the situation making it an almost polar opposite to the regular series. Having the enemy fleet ‘fully‘ show up and getting planet-side again with no objective and no weapons *chef’s kiss*.
4 was my most disliked, I like the story bits with Chief and Cortana and they were great, but everything else just felt like a by the numbers plot and the villain sucked. I liked the fact I could sprint, but the flying enemies just got obnoxious, 5 had them too but you could generally take them down faster.