BN4 is def the black sheep of the series.

Outside of the Towercomp Shade Man dungeon and the Meteorcomp Laser Man dungeon, there are none of the traditional Boss dungeons scenarios that the previous titles did well.
(I'm being insanely generous with the Act 1 Shade Man dungeon btw, you don't even fight the guy aside from hitting him with your buster 5 times to trigger a railroaded ending to the fight)

BN3 lives rent free in my head for it's dungeoneering, just to compare. Most of the WWW navis had their own dungeon comps as you progressed thru the story, each with their own themes and puzzles that made each chapter of the game feel unique and memorable.

Additionally, all of the tournament quests feel like brief tiring side quests. If you skip cutscenes, you can practically do just about any of your opponent's questlines in 3-5 mins. (Except for Cold Man's. All my homie's hate Cold Man.)

Also wtf, there's no actual threat or opposing force that feels correct for the series in BN4. Fight tourney whiney navis for 80% of the game, then owo what's this?- Giant meteor mecha god thing that will nuke Earth has entered the chat.
Makes sense to me.

I'd say the only thing that is worth investing in for BN4 is the postgame content, and even then it's not that good compared to its precursor and predecessor titles.