1. 'Do not burn' option. Option that will let you capture enemy buildings/people instead of burning everything around. For
example: if you capture enemy Fortress you also capture territory that 'belongs' to that Fortress and also buildings/people/resources.
I think this was already suggested a long time ago. Yeah it would be great to have it as an optional feature, although I like the way
S2 just destroys everything. Instead I'd suggest an "instant destroy" option where you don't have to wait for the buildings to burn
down, because in the middle of a fight, time is quite essential.
2. Advanced Trade Routes. You are able to create 'trade routes' between storehouses (your and your allies). To exchange goods
you will need... donkeys ;) (in a similar way like in Settlers3).
As I'm not a big fan of S3, I don't really like that idea. Trade routes with your allies however are possible with the current nightly
versions of the game, not sure about the "stable" releases though. It's still buggy but works most of the time if both of the
storehouses aren't too far away from each other.
3. Residences. People are so cheap in Settlers2. Too cheap in my opinion. I prefer the Settlers3 solution for 'creating' people.
Residences, special buildings that will 'create' people. This time the 'created' people should just stay in a residences till they will
be needed for something (just like in headquarters). (residences also should require food in my opinion).
That's one reason why I don't like S3/S4 as much as I do S2, because it just annoyed me to build & destroy residences again and again.
4. Copper mine. Copper should be required to create Tools in Metalworks. In my opinion we should just complicate the economy in
S2 because it is rather too simple.
This would render most of the maps that are currently in the game unplayable, so I don't like it. A better way would be to make the
metalworks use iron & coal like in S3/S4 in my opinion.
5. Sulphur mine. Sulphur should be required to use Catapults (Stone+Sulphur) because Catapults are powerful but cheap. Sulphur
also could be useful in...
The same thing I wrote about idea number 4. The current addon which just allows the building of a limited number of catapults is a
better solution for this problem IMHO.
6. ...Ship fights. It would be totally awesome if you would be able to do ship fighting in this game. Because now all we can do
with ships is to transport goods and people and that's not very realistic.
That would be a great addition to the game in my opinion because it would make the sea maps more interesting to play, because you'd
have to secure your ships with additional warships.
No offence intended with my answers, but it just reflects my opinion on certain things ;)