I updated my phantom 4 with the latest firmware and tried to shot with 1080p, 120fps. The video was blurry and super slow. Anyone having issue like mine? and the horizon is tilted.

Did you use 1080/120 prior to the upgrade and are you comparing the before after results?   The whole point of 120 fps is to create slow motion video so if it's running slowly, then it's doing what it's supposed to do.   Also..  To accommodate the higher bandwidth required by 120 fps, the resolution is lowered somewhat, so it won't be as sharp as 30 or 60 fps.

The tilted horizon is another issue not related to firmware or video mode.  If you browse through the forum, you'll find lots on it.

Can you post a video clip.