The call of Rapture was just far too strong for me and overwhelmed my cynicism of the game. I have to say that right now I'm extremely glad of the fact. Dual-wielding plasmids and a gun is sooo much better than switching between the two in the first game. It's also damn near essential once the insanely quick Big Sisters get involved. The game is also much, much scarier than the first game because it uses some great survival horror tricks. Ammo is far rarer than it was before, enemies have a habit of coming out of nowhere and there can be long periods of time where there are no enemies around. Then there's the audio, the music is one thing but then there's the idle chatter of splicers who haven't seen you. The whirring of a security camera and the clanking of a Big Daddy add to the atmosphere more than the first time. Then there's the terrifying shriek of a Big Sister, trust me when I say if you're low on ammo and health when you hear that you will start to panic.
BUT there are big problems too. Hacking is now piss-easy to the point where pretty much every vending machine coughs up free ammo and medkits. Then the remote hack dart turns every camera and turret into your willing slave. This basically means that I'm less moving through and surviving Rapture and more taking over territory. I also discovered that it's pretty simple to always have security bots following you. Hack something near a bot shutdown panel and screw it up to release bots, run to the panel to shut them down then hack them to take them as your own. Thankfully Big Daddies aren't even slightly fased by bots, swatting them out the sky like giant flies.
Bottom line, Bioshock 2 is worth your time if you enjoyed the first game. The story may not be quite as good, but the improvements to the actual gameplay easily balance it out. Go play it.
Also the video research camera owns the original research camera so much it's embarassing.
Also again I had a great idea for a possible Bioshock 3. I may put it into a cblog or some fanfiction at some point.