I bought Dark Souls last year when the PC version came out, the game was great but was a bit of a bare-bones port from the Xbox 360 version and the PC controls were not as great due to the lack of time they had in porting it. ( remember that they also made additional content for the Xbox and PS3 versions at the same time )
Dark Souls 2 will have a PC version on release ( or at least soon after ) that should make playing with mouse and keyboard much easier. Instead of going to a new universe with their new game they are making it in the Dark Souls universe, unless they are going to change things drastically then there will be a lot of subtle references to the first Dark Souls game and hopefully expand on the lore and leave many new questions in our minds afterward. The story and lore for Dark Souls has to be one of it's strongest points. Very little is simply handed over to you through a cut scene or dialog, and a lot goes unexplained and it is left to your imagination and detective skills to link it together.
The gameplay should be similar to previous Souls games, most similar to Dark Souls of course, changes to expect may be in the magic system and some combat and movement changes similar to the differences between Demons Souls and Dark Souls. It is similar to The Elder Scrolls series in that it will release a new game in the series that is generally an improvement over the previous games, if only in small ways.
I highly recommend getting a PC compatible Xbox controller for these games, as that PC controls in Dark Souls were a little awkward for me. Http://www.mightyape.co.nz/product/Xbox-360/PC-compatible-Xbox-360-Wireless-Controller-Black/1541122/
For anyone who enjoyed Dark Souls this would be a must have.