Please note I hated Reach, Halo 3 was alright but nothing special. I'm a fan of Black Ops and COD in general.
Halo 4 is mind blowingly awesome and is probably the best firt person shooter this generation. The graphics in multiplayer rival graphics in most games sinle player mode. Everything is high resolution, textures are very clean. Playing on a 50" Panasonic Vierea 1080p Everything is fast and intense like COD, but with more weight. Reach and Halo 3 always felt too sluggish to me. Loading times between matches are killer fast. This is pure enjoyment.
Playing the campaign brought back memories of playing the original Halo, the awe and astonishment was there consistently. I had the same feeling the first time I played Perfect Dark on n64, feels like a real sci-fi world.