One thing I will say for Halo 5 is that it was one of the more enjoyable ones to play (solo) on Legendary, but the story was a bit lacklustre and it was over pretty quickly. There seems to be an annoying trend in movies at the moment that makes the story suffer, to set up the sequel, and I get the feeling Halo 5 suffered from this too. So, while I did enjoy the game, the story didn't blow me away and I'd say its the worst Halo of the lot :s.
3 is my personal favourite, with 1 being number two and 2 being number three XD. I actually quite liked 4, while it did change some things and avoided the rings entirely, I thought it wasn't a bad attempt at 343 trying to start a new storyline off, and I'd actually recommend it - which I would find much harder to do with 5 personally. When 6 comes out, I will probably end up getting it, but I won't be looking forward to it as much as I did the previous ones :/