I think it gets boring when you start to know exactly what you can get away with....I can look at a situation on radar or plot, check the weather and tell you whats going to happen 99% of the time, before I do it.
We know how far the AI can see/hear.....mostly.
We know our torps are going to run true, except the very rare circular
run (I've seen 3)
We know if we crash dive that we can pull out of it....every time.
We know if we order periscope depth that we won't keep rising and broach.
I LIKE the fact that you can take a Balao past 600ft and start to lose it(depth control).....I think Ducimus called it a bug in TMO, but I think that possibility should exist for every sub that goes past 300-400 ft......
I'm on patrol 17 on my current campaign- 80+ ships down, well over half a million tons(not exactly historical, eh

) -I haven't reloaded games or "cheated" with the cams in any way, and I only had one time where I took damage (from a deck gun

).
I think the last time I got REALLY worked up and adrenalized was around Patrol 11-12. I got a message to intercept a BB group and actually found it

BUT......with flat, calm sea conditions, clear and 2 hours until dusk.
I thought making an attack was a suicide run. BUT, I also thought that any real sub captain would consider it his duty to try.....so I sank a Kongo and stayed up until 2 am making my escape from the escorts who wouldn't give up, but never did hurt me. I liked that one, I expected to get sunk and I got away.
Sinking a ship should be a MAJOR accomplishment.....that Kongo was a big deal to me, my first dozen using manual targeting were big deals. TMO made it exciting for a long time, but I'm pretty much getting the hang of it. Good thing for me that its almost RL hunting season and I'm ready for a break......I'll start back up fresh and get my ass sunk.....