Maybe in an ini file have a bunch of starting options.
Number of starting dwarves
number of starting points
immigration rates
stuff like that. That way people who want it a little easier can make it so, people who want it harder can make it so. Letting the user change options does HUGE amounts of help for replay value.
For my self, it's not about hard/easy, it's about what type of fortress I invision.
I'm not interested in going too deep, or even crossing the river. For me I just like making a little settlemtn for 10-20 dwarves and being content with that, and just watching and tweeking. I like to micro-manage and detail everything. I like to be able to know the names of all my dwarves rather than faceless masses. This is all posible with some simple options.
I don't want immigration OFF, I just wish I could control it more. I've never had nobles or book keepers or any of that advanced stuff. I just like mining and crafting. I wouldn't want to be totally cut-off from immigration, but I really don't like my population doubling every year. Like I said before, I can handle it, I can put them to work, but I stop having fun at this point. Maybe my friends are all similar in interests to me too, as they all express they stop having fun after about 1.5 years.
If you love nobles and 50+ populations, that's great. But there's no reason a game like this couldn't be flexible. I really really love this game so much. The ONLY thing holding me back from not starting over and over and over is immigration. I've never played past the 2nd spring because I just get overwealmed. Not litteraly as in I can't feed everyone, but just from a management perspective. Maybe if the interface and labour stuff was easier (like an at a glance list of every dwarf and all their current skills/work assignments rather than just a list of their main skill). But even so, I love this game because it lets me create a cool initial group of dwarves. I want to see how rich and happy I can make those initial dwarves.
Maybe adding 2-3 dwarves a year I could handle, as it would give me time to get to know them.
For me the best solution would to have immigration tied to the trade screen. Every time the yearly trader comes, you tell him how many immigrants you would like. This is realistic as the traders are the ones who spread word of your settlement back home. So you tell the trader how many immigrants you want, and some time that year, a number close to that many arrive.
This way you have to plan for the whole year in advance. If you think you can handle a lot and select "maximum" or what ever, but find you can't, you're still committed to that number.
If you select 'none' or 'few' then you're stuck with that amount untill the trader visits you again.
The trader is your only contact with the outside world, so it would make sense they were who you told if you needed/could handle/want more dwarves.