Well if you are considering to buy BS2 you best make up your mind quickly as today is the last day of the sale. It's on a hefty discount, costing only $19,99 right now.
The biggest differences are most likely the graphics (cockpit shadows, missile trails etc). The Helicopter wingman AI was also massively updated compared to the original black shark.
Naturally you can take advantages of the other advantages in DCS world, these include:
- Much larger terrain to fly through compared to the original BS1 game.
- Much larger selection of AI assets available
- Much more capable mission editor with many new functions
There are also Ka-50 campaigns that are not available in BS1. I believe "Medvedev-2" is a new campaign. The old campaign "Georgian oil war" was massively updated compared to black shark 1. If you so wish, you can buy the "republic" campaign only for BS2.
If you have or intend to purchase the Nevada Test and Training Range or any of the other new upcoming maps, you can fly your Ka-50 there if you have BS2.
One of the biggest issues I had with BS1 was the fact that it only had a russian pit with a russian voiced betty. I do not know if that is an issue for you or if there are any mods available.