To keep things simplified, I made the review into a list:
Game Mechanics:
-Average graphics
-Texture loading problems
-Great sound
-Same lovable Rapture scenery
-Maps still feel somewhat new despite this being a sequel
Plasmids and Such:
-Dual wielding is amazing
-A few new plasmids and old plasmids have new upgrades
-Gatherer's Gardens have so many more choices
-Gatherer's Gardens and Gene Banks are far more common
Combat and Such:
-Gathering idea is incredible
-There is actually a reason to harvest little sisters (so you can just skip gathering)
-Waves of splicers make you feel like a powerful Big Daddy, without making you overpowered
-Same old weapons, just redesigned for a Big Daddy
-Big Sisters come at the worst times (which is a plus)
-No boss battle
Multiplayer:
-Often very slow paced battle
-Poorly animated models
-Great plasmid and weapon choices that allow for combos
-Higher levels are overpowered
-Too many noob tubers
-Very, very bad matchmaking system (teams are often unbalanced, hard to join games)
-Soooooo buggy
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Now the big one:
Plot
The overall plot of Bioshock 2 was far weaker than in the original. There aren't as many side stories, and the few that there are just don't seem as "powerful" as in the first game. The story line was a lot more linear than in number 1, which is good and bad; the game is a little shorter, and there are not a bunch of twists, but it is a lot less annoying (aka "Go through this door" means walk through the door, not get close, have it collapse, and have to walk 50 miles around rapture to get to the other side).
The main story of Sofia Lamb feels out of place to me, simply because 2K tried to throw her into the original story and make her one of Ryan's big oppositions like Fontaine (but of course in the first game you never hear anything about her). However, I do like how they include Sinclair from Sinclair Solutions that you heard so much about in the first game.
The biggest problem I have with the plot, and what I think makes it weak, is Sofia. She has a lot to say about creating a Utopia and making her daughter perfect, but none of it sounds nearly as ideological and amazing as Andrew Ryan. One of the largest and most meaningful parts of Bioshock 1 was Andrew Ryan and why he built Rapture. Basically, everything that man had to say was pure genius. But Sofia Lamb, ehh. She had some good points, but never once sounded as good or was as smart as Andrew Ryan.
Overall, the plot comes down to the whole thing about free will again. In Bioshock 1, you didn't have any free will and just did everything that started with "Would you kindly." In the end, Andrew Ryan had his epic speech about free will and asks you to kill him, and you are forced too without free will. In the second game, Eleanor Lamb doesn't have any free will because her mother (Sofia) is keeping her hostage in a sense, and you have to go free her and give her that free will (except without the epic speech).
Both games were great, but Bioshock 1 definitely wins in the plot section.
Oh, by the way, the ending sucks - no twist or anything. Good cut scene at least.
