They are sticking with Hetty for far to long.

She's a fantastic character, but Linda Hunt is old and well past retirement and by sticking with Hetty as the main background storyline, they are stuck with a mystique that's already been mostly resolved and the part that isn't, simply isn't that interesting, especially since there's no progression in it.

They need to bring Hetty to a conclusion (which they seem to cowardly to do) and start up a new background mistique.

The Admiral has some shared history with her, but as we've found out through the years and even in this crossover, has plenty skeletons in his closet that aren't related to Hetty.

G still has plenty skeletons they can use from his CIA days.

And Deeks was an undercover cop for a long ass time, which they used a couple of times, but could be used in a variety of other ways.

They should also either supplement the team or replace some of the young blood with someone who brings their own history.

In NCIS, bringing in an old FBI agent allowed them to bring various blasts from the past from his career into the show already.

For Hawaii, they made the mistake of making the whole team rather young. The team lead has some CIA history, but that's about it for them.

Shows like this need the weekly procedural supplemented with good long term spook or skeletons from the past threads running through it and currently all 3 shows are missing that.

They tried to improve on that with this crossover session, which blew its load in a single week across all 3 shows.

They should have dropped some hints and threads across all 3 shows starting a year ago, to then culminate into the crossover.