45 considering I bought it, yes for as long as you like games like this. In terms of replay-ability
It currently comes with a scenario editor which lets you make a ton of changes to how you start and other things
It has 5 or so difficulty settings
plenty of biomes that have different problems to overcome but max and min temprature is also location based (jungle = a lot of sickness, desert= very little trees, etc, etc.)
There are 3 so called story tellers which you can choose from which changes which/when the game throws events at you
It has also an very good mod-api. In fact every bit of content of the game is written using the mod-api. (The game is even listed as a mod in the mod load menu)
It is also still in alpha and it is still getting worked on. However, despite being in alpha except for a weird sound problem that sometimes happened the game has had no problems at all. This sound problem may or may not be fixed by now as well.