I'll tell you one thing. A lot of guys in the nuclear world would kill to get an operating job at a hydro plant. I'm not trying to discourage you -- but you might have forgotten that there are a lot of the hassles that non-nukes don't have to deal with. I'm not sure how the pay compares, so that might be a big factor in your decision. But hopefully it's not the only factor. Also, if you're a control room operator and planning on starting out as a non-licensed field operator at a nuclear plant, the (initial) pay difference can't be too different I wouldn't think. Afterwards, it will take some time before you build the seniority and experience before you can get into a control room license class. But it can be done!
Differences:
You will be hired with a group (most likely), and you all will be required to maintain a certain level of progress. It is true that the process is more controlled; more structured. The plant obviously does not move much and surveillances, work, and other evolutions are scheduled many weeks in advance. For one example, you'll all be required to learn to operate the emergency diesel generators, and during one monthly set of surveillances you'll probably have most of your class all taking turns under instruction. If there happens to be a forced outage or a planned refueling outage during your quals, you'll all be doing certain tasks in a planned, scheduled manner. There is no such thing as having the plant manager come around and trip the unit for operator training; doesn't happen. We try to stay at full power for an entire operating cycle; two years. Naturally, even the experienced people get pretty rusty on doing things that were routine on Navy plants (now, how do I draw a vacuum on the main condensers again??). To balance this, plant procedures are very detailed with some good operating information in them; with a system drawing and a procedure it usually isn't difficult to figure out a task, even if you haven't done it before.
Quals are "task based", which is a difference. You'll remember, in the Navy, the focus of many quals was system based. There is some crossover, but you'll find that the qual cards are mostly filled up with sign-offs on tasks -- perform a waste gas release, swap pumps on the degassifiers, perform a service water pump surveillance -- that type of thing.
Eventually, you'll get fully qualified on all required watchstations. Depending on the location, that will probably be 3 to 5 watchstations, and you'll likely have to qualify peripheral things such as fire brigade member, etc. You'll find yourself standing Conventional watch, and have a coverage area about ten times larger than anything you did in the Navy. At times, it is physical; you'll probably walk 3 or 4 miles on rounds every day you have the watch, and you'll have the watch most every day.
If you're thinking that a commercial nuke is somehow more lax than the Navy, you would be wrong. Many things are scrutinized heavily, and operators must learn to live with that. You got out of the Navy about the same time I did; I felt I had much more freedom to operate independently when I was in the Navy. In a commercial nuke, you will do almost nothing without someone looking over your shoulder -- and then offering criticism afterwards. You'll do pre-job briefs till you're blue in the face and then do post-job briefs, even on the simplest of tasks. That's just the way it is. I'm guessing that in the hydro plant, you start up, shut down, and parallel generators all the time, frequently with little or no supervision. That would never happen in a nuke plant.
I hope I did not focus too much on the negative. Yes, the challenge is definitely here. The career path is here too, especially for an operator. I started as an NLO and am now an SRO. For the most part, I really enjoy coming to work -- because of the challenge, because it is usually interesting, and mostly because I work with outstanding people all around. In whatever you decide, good luck.