Won't give you the same sense of amazement as its predecessor, but still a wonderful game and definitely worth the money
The combat mechanics received a pleasant tuneup; we see the welcome return of weapons like the crossbow in the form of the harpoon gun and the grenade launcher, as well as new additions like the rivet gun carried by the Big Daddies in the first game. Weapon upgrades are available just like in the first game. One of the coolest new tools in Bioshock 2 is the remote hack, which fires darts at devices so you can hack from a distance. This brings me to the hacking mechanic which has been reworked altogether. We see the abandonment of the pipe puzzle used in the first Bioshock for a reaction based system which, unlike the puzzle, does not pause the game while you are attempting the hack. It involves a needle moving across a bar, with the objective to hit A while the needle is in a Green zone. Hitting a red zone triggers an alarm, and if you hit a Blue zone it has the same effect as Green but adds an extra bonus to the hack, different depending on the machine.
The research camera makes another return granting similar effects, and the occasional tonics, just like in the first game. However the way it works is much cooler and more interesting. Instead of just snapping the three or four pictures you would in the first game, instead you use the camera on an enemy and it begins filming as you kill it. Repeated killings in the same method, like just using the rivet gun, produces progressively lower grades of research. The basic plasmids are the same, as well as the tonics, but in Bioshock 2 you can upgrade to have a hell of alot more tonics equipped at one time; and considering the difficulty at some points you're going to need them. In addition to the basic effect of the plasmids, they each have two upgraded levels; the first providing an increased effect upon charging for a few extra seconds, and the second making the level two effect standard and the charge effect even better. Almost every plasmid from the first can be found in Bioshock 2, and the few that aren't are replaced with something of equal or greater value.
The one way in which Bioshock 2 one-ups the first game in a manner OTHER than its mechanics is the increased number of moral choices. In the first game you killed a big daddy and either saved or killed the little sister, big whoop. In Bioshock 2 on the other hand you have a little more freedom in this, you kill a big daddy, then get to decide to either harvest her on the spot, or take her around with you and have her harvest some adam off a dead corpse while you defend here. If you go with the latter, you then still get to decide whether or not to save her. While this might not seem like a big deference, but something about the game's having you protect the little sister makes it feel a fair amount more evil should you decide to kill her. In addition to this you get a few other moments of kill or not to kill, I'm not going to give anything away but each one presents a different situation that gives you a real feeling that your choice has some impact on the story *WINK*WINK*.
Now up to this point I've said almost nothing but good things about Bioshock 2, but it's not perfect. I'm not sure if it's because I played this game nonstop, or because I've played the first one and was able to play get good at it faster, but it seemed a good helping shorter than the first game. I'm not saying it was way too short, but It was just a tad on the short side. This is not in all ways a bad thing, because had it been as long as the first game I have a bad feeling It would have felt too long. This is because the game does feel really really familiar if you've played the first game, and while it is different enough that it doesn't feel like more like an expansion than a sequel, I do wish that Bioshock 2 had the same spark as first Bioshock.
On a completely different note, I haven't played much of it, but I was pleasantly surprised with the multiplayer mode of Bioshock 2. When I first heard there was going to be an online multiplayer mode in Bioshock 2, I thought It was going to suck, really really suck. But much to my surprise I found myself not completely revolted. Theres a couple of different game modes including free for all team combat, capture the flag, and king of the hill. (each by some more Bioshock themed name) Your player gets two weapons of your choice, two plasmids of your choice, and three tonics. The weapons are all from the first Bioshock, and the tonics are all similar to those in game but adapted for the multiplayer mechanics. Unfortunately almost all of these are locked to begin with but you'll start unlocking them after only a few rounds.
Overall I think Bioshock 2 is a really great game, but if you try and hold it up to the pedestal of the first Bioshock, you're going to be disappointed that It'will fall a bit short. But again I must point out that this is mostly in part to the fact that Bioshock one introduced alot of new things that created a sense of wonder, and if Bioshock 2 tried to make up enough stuff to come even with that it would be a pile of **** Bioshock 2 takes the great concept of the first Bioshock and adds just the right amount of twist to make a great game, even if I would have like to see just a little bit more. My final statement is, if you liked the first Bioshock, buy the second.