If you play Halo 4 directly after playing Halo 3 (something I did after getting the Master Chief Collection on PC) makes it so apparent how much of a huge step backward it is in terms of continuity, storytelling, and overall balance.

Mechanically, Halo 4 plays perfectly fine. However, the weapons are a huge step backward, as all of the Forerunner weapons are just human weapons with a metallic skin and orange lasers. They even reload like human weapons, which was a huge step back from all of the unique weapons they introduced in the original Halo trilogy.

The only actual new thing they introduced that was cool was the mech, which you didn't even use much in the campaign. If Halo 4 came out after Halo 1, I think it would have been an awesome game. But it had way too many step backwards compared to Halo 1 - 3 + Reach, especially when they did the story pivot instead of having it humans vs Covenant vs Forerunners, they turned it into another humans vs Covenant + Forerunners again, and that just made it really lame, as the best moments were when it was a free for all and felt like all out war.