[GrimmSweeper]

The bank heist will definitely start losing its lustre after repeating it several times over. For me, it was the waiting for long periods at two points with very little variation in what happens to you. It is probably the weakest of the missions you can do. On a scale of fun I had while playing it was, least to greatest

Bank Heist -> Doublecross on Busy Street -> Bridge Prisoner Rescue -> Panic Room Heist -> the two Hard missions.

You don't need to level up particularly high for Hard difficulty, particularly on your own with AI buddies that do a good job of killing baddies; they seem to have unlimited ammo and precise aim. I tried my hand at one of the last two when I was level 9 or so. Failed, but still enjoyed myself enough.