Going to have to add to the chorus in favor of the drill. Wrenching through Bioshock 1 was goddamn irritating - it was the best weapon, but sadly was no goddamn fun to use. Repetitive though it may be to throw a lightning bolt and then literally jam my drill down a mook's throat, it's still goddamn entertaining. Basically once you get the drill dash there is no reason to use any other weapon.
Much like in the first game, most of the weapons seem needlessly weak and most of the enemies move around too much so you're basically wasting an insane amount of ammo. The total inability of most enemies to sit still makes the rivet gun almost useless by level 2, and the only useful ammo, trap rivets, end up becoming useless by level 3 simply by virtue of scaling hp going up too fast. The Shotgun's effective range is pitiful - basically melee only - and the spear gun reloads so slowly and requires such precision to be useful that without shocking your target first, it's also not that great. (But it IS satisfying.)
The machinegun is my favorite. The tommygun in Bioshock was horrible, but the heavy machinegun in Bioshock 2 is fucking amazing. Once you get level 3 electro shock you can hose down enemies with lightning at the same time as you unload the ammo in your gun. A fully upgraded gun + lightning with eve cost reduction tonics will kill a big daddy or big sister before they can even move. Also, if you use the research camera it brings your score up FAST.
Also if anyone has trouble protecting little sisters during adam farming, drop down three mini turrets and stand in a corner. This works until the last two levels, at which point you just need to provide minor fire support.
I just beat the game, as far as single player FPSes go the game had a reasonable length. I don't generally replay FPSes, but I could see challenge/achievement runs being worthwhile simply because Bioshock 2 is actually, you know, fun. It was interesting to see some of the additions to Rapture's history that they added. It's a bit of a plot hole that a character as important as Sofia never gets mentioned during the first game, but it fills the gap of public opposition that Ryan didn't have before, as Fontaine's war was mostly behind the scenes. Bioshock 1's plot was... hokey. I felt like the setting was amazingly well fleshed out, but the main character didn't make any fucking sense, and the actual characters themselves didn't act with believable motivations, with the exception of Tenenbaum, and even then. (for example, not revealing atlas or trying to wipe the mind control despite knowing about both of these things from the fucking start) Bioshock 2, I don't know, maybe they fired their shittier writers?
I only have three beefs with the writing - there's no real explanation of what happened during the years between the end of Bioshock and the beginning of Bioshock 2. How the hell did these people survive? The splicers are clearly more disfigured from drug abuse, but that seems to be about it. You'd think that at this point everyone would have died, or they'd have been caught going to the surface or something. I would have liked to have seen parts of Rapture that hadn't succumbed to splicing and decay as rapidly as the rest. I always felt this was lacking - everywhere you go, there's leaks, things are on fire, people are dead, and it was like this in the first game! If there's no stability and things are falling apart faster than the Big Daddies can fix them, how the hell has Rapture not completely collapsed into the trench at this point??? Beef #2 is that Subject Delta's backstory is lacking. The writers said they did this because they wanted players to identify subject delta as themselves, but as a character he was compelling, and I spent the whole game waiting for a reveal that never came. My last beef is the ending - I got the best ending, but I was still pretty disappointed. I can't see any other way it could have ended, though, so I guess that's just me being sour.