The combat is similar to DA:O, just faster and better balanced (well, and easier, but you could always increase the difficulty setting). I honestly can't understand people who call DA:O a deep tactical reincarnation of Baldur's Gate and DAII a stupid hack-and-slash. It looks more flashy, but is about the same.
The story definitly is less epic than DA:O, but i found it more interesting. Some things could have used a bit more explaination, but i never found the "plot holes" some people seem to see. Every companion has an interesting story, and they participate much more in the main story than in DA:O. The "villians" also have more personality than in DA:O (where only Loghain was really interesting in my opinion).
So, i like combat and story much better than in DA:O. That's not to say the game doesn't have some problems: The level design is weak. And while DAII shares this trait with it's predecessor, there is also much recycling of dungeons. While the combat itself is better, enemy placement is often annoying. Kill a group of enemies, and a second wave appears, sometimes without a good explaination. Both problems are fixed in the DLC's, so Bioware at least has learned it's lesson.
So if you like DA:O, i'd say get DAII. Maybe you'll receive it like me and love it, maybe you'll see the alleged flaws that apparantly make it the worst thing since the blight. For a budget price, i think it's worth trying out.