One of the big changes in DF2014 is that world history no longer freezes in time at the end of world generation.  As you play the game, there are background events occurring where armies continue to march, NPCs continue to interact, etc.  One side effect of this is that the larger map sizes will run much slower then before, so it is better to play on small, smaller or pocket sized maps.

Personally, I try to generate worlds with micro-regions, which makes it easier to get two, three or even four different biomes to mix together in interesting ways.  In order to do that, I have to edit the data/init/world_gen.txt and create my own custom world.

For example, by default the "SMALL REGION" recipe produces a 65x65 region world with about 250 different regions.  With some tweaks, you can make the world much more patchwork so that it has ~1100 different regions, and it should be possible to get as high as ~2500 different regions.

First, you should edit your data/init/d_init.txt file and enable logging of world generation rejects ([LOG_MAP_REJECTS:YES]). This will let you quickly figure out why a particular profile is resulting in hundreds or thousands of rejects.

Secondly, you should make a copy of an existing region and paste it at the end of the file and edit that instead of the original definition.  You can leave comments for yourself because Dwarf Fortress ignores anything not enclosed in square brackets.  Putting the whole directory into a version control system like git or subversion can be useful as well.

You will immediately want to change your [SUBREGION_MAX:####] setting in that profile to the maximum of 5000.  When creating patchwork worlds, you are going to be bumping up against that limit frequently if all goes as planned.

There are two sets of parameters that control how fast features change over distance:

#1 - Look at the first number on all of the "_FREQUENCY" lines.  This controls the mesh size of the world.  By default, the mesh is set to disabled, but you will want to bump this up to 4 or 5 for small/smaller/pocket worlds.  For medium/large worlds, a setting of 6 or 7 might work better.

Mesh size is a complicated topic.  You should pick a reasonable value, then leave it alone until you have generated dozens and dozens of worlds and run out of room to adjust the second set of parameters.

#2 - The other set of parameters controls the minimum/maximum values plus how fast things can change over a given distance.  Higher numbers result in a more patchwork appearance, lower numbers result in a much smoother appearance.

(these are "SMALL REGION" defaults):

[ELEVATION:1:400:202:202]
[RAINFALL:0:100:101:101]
[TEMPERATURE:25:75:101:101]
[DRAINAGE:0:100:101:101]
[VOLCANISM:0:100:101:101]
[SAVAGERY:0:100:101:101]

Be cautious when changing the min/max values (first two numbers), they can result in huge numbers of rejected worlds, biomes that cannot exist at all, or other problems.  You should leave these alone until you have more experience with world generation.

The last two numbers on each line is what you want to play with.  The limit for these values are 0-3200, with the second to last number controlling east-west and the last number controls north-south. The default values are pretty conservative.