Nightmare mode is thus far unforgiving but fair. Battles are made unnecessarily even more difficult by my chars ignoring orders given in tac cam which I've had to use extensively. Tac cam itself has some annoying issues, like zooming in on your characters each time you select them. This means to give orders to your entire team you have to click one, drag camera to enemies, click next, drag camera to enemies... ect. The tac cam itself feels ackward and if you like swapping in and out (as opposed to just unpausing in tac cam and staying in that view) you have to resect your character, realign the camera (it doesn't quite do it for you) and then come out of tac cam.
There's also some crazy bugs. Had a tutorial thing stuck on my screen forever... persisted through reloading, computer restart, ect. I had to remake my character... in that new file Cassandra did not give me the starting set of health potion she was supposed to give you. Great.
Saying all that I've extremely enjoyed my time in the game and say it was worth the wait 100%. Far far from perfect, of course, and there are a lot of annoyances. For example I can already tell the crafting (the actual process of putting the collected crafting items together) is going to get incredibly tedious. There's a video explaining why, and having messed with it myself I agree wholeheartedly. But they're just that; annoyances. The core game itself is incredibly fun and I'm enjoying the story so far, which has a nice prelude feeling to it where all the little tiny pieces add up to form a real plot. I know a lot of reviewers said the start pretty much sucked story wise, but I've read slower books so maybe I'm unique in that regard. Besides, Suikoden V had one of the darn slowest starts in existence and remains one of my favorite stories in gaming.