>>534934860
Halo CE was one of those games back then that you had to experience yourself to "get it", nowadays its just an okay shooter with some decent story and nice music. Weapon balance exists and each weapon has a specific thing going for it (the noob combo is the go-to option for obvious reasons)
Halo 2 was rushed and is notorious for having shit boss fights, sniper jackals, and some other set pieces.
Halo 3 is arguably the best one of them all, and also makes for a solid COOP experience.
ODST is Halo 3 but instead of playing a SPARTAN you're playing "the best of the best" in terms of regular human soldiers. Fun game, music is good, the characters have some good lines to say.
Reach was the "bon voyage, suckers" call from Bungie before they went on to make Destiny. Its an okay game and really gives you the feeling of "we are fucking losing this planet, holy shit".

Just buy the MCC at some point when its on sale and ask somebody who played halo before to play COOP with you, or play it solo on Heroic (the intended way)

CE > 2 > 3 > ODST > Reach >>>>>>>>>>>>>>>> 4
In order of playing games.
Fun factor?
3 = ODST > Reach > 1 > 2 >>>>>>>>>>> 4