For readers who've never played through Dragon Age: Origins, I can summarize that game as being a wonderful romp through a dark fantasy world where your choices shape the epic story of a heroic main character vs. the forces of darkness. Pretty fun, right?!
Dragon Age 2 didn't have the same punch for me as a gamer since the protagonist, Hawke, is left by the writers in a bit of a lurch; in the first game, the antagonists were extremely clear: you have to defeat the Archdemon, and to do that, you have to wade through waves of Darkspawn, and to do that, you're going to need to unite Ferelden under a single banner on your side. The way you may accomplish it is pretty straight forward, but peppered with your choices that make it unique each time. Dragon Age 2 does not have a clear antagonist for the majority of the game play, which leaves players who are looking for a great story driven experience in a bind about why they are rooting for Hawke, if there's no one to root against.
You do still have some fun side characters and quests, but the story driving Hawke is about becoming the Champion of Kirkwall, which by the end of Act 1 you'll believe means he/she's the errand boy/girl of Kirkwall. All the way up to the final battles of the game, you'll have to choose sides for different elements and factions in the story, but no matter which side you choose the battles end up being the same since even if you choose to side with Faction A, and fight Faction B's boss, you still have to fight Faction A's boss a few minutes later.
Speaking of fighting, the combat is pretty delicious. If you played Dragon Age: Origins, the original classes are still there, if a little bit more simplified. The fun part is the grand animations, explosions, particle effects, and speed at which the main game plays now. Pausing for tactical commands can be a huge joy, since you may freeze the frame on some incredible action, and spin the camera around for some very Matrix-y effects shots. And of course, you can still switch to play any character in your party during a battle, so it still pays out in big dividends to pay attention to how you level them.
Still, if you're anything like me, by the end of Act 1 you're going to be pretty sick of seeing the same environments over and over again, regardless of the snappy combat, and be wondering what the point of moving forward with the plot is. Without any spoilers, all I can say is that for this game to be fun, you're going to have to find ways to invest in the characters you are presented with. There are some fun side quests, witty banter between companions, and awesome combat that can hopefully keep you driving through.
In the end, if you're a fan of Dragon Age, go ahead and buy this game. Just be aware that unlike the first, there's no overarching bad guy(s) to pursue and feel threatened by, which takes some of the epic-ness away from this game. However, if you enjoy the Dragon Age style of fantasy combat, that can help pull you through the story and make the game a worthy investment.