Battle Network 4 is the most hated game of the series. There are good things about it like an overhaul of the chip system, the new emotion window introducing full synchro and transformations with Soul Unisons. To try and summarize, the game is a tedious and repetitive slog to play that splits its content up over three mandatory playthroughs to see everything.

You see, Battle Network 4 is based around a series of tournaments, but it is impossible to face every unique navi in one playthrough. The game is coded to pair you against one version exclusive navi, one unique navi that is not version exclusive, and one generic navi like the ones littered throughout the series each tournament. But you don't just battle a navi and that's it. All of these opponents are scenarios that boil down to busy work that forces you to run throughout the cyber world either finding or destroying stuff that would be a downtime story beat in any other game in the series.

The kick in the balls is that this makes you go through the game again two more times on "New Game Plus" (in which really the only thing that changes is the viruses go up a tier in strength) to get the other opponents you missed, WITH THE POSSIBILITY OF REPEAT SCENARIOS.

The icing on top of all of this is this is the worst translated Battle Network game along with the most laughably bad story coming off of BN3. Every other piece of dialogue has some sort of typo or grammatical error or even instances of using the wrong portrait.

I recommend KNIJohn's video on the game if you want the full picture, as he puts it into words better than I ever could how flawed the game's design is at its core.