I honestly lost track of time. Classes were canceled and I couldn't go outside because of the snow, then internet went out, so it was having nothing better to do. I'd say it is shorter than the first game for sure and far more linear. Then again, I can't imagine how much of my Bioshock 1 time was spent rearranging pipes, so it's hard to do a fair comparison. It feels like an expansion pack for sure.
Also, for those saying the drill isn't powerful, the game even acknowledges that the drill is a beast with all the tonic slots that make it more powerful. You have the "Power to the people" upgrade, the big daddy research upgrade, the tonic slot upgrades, then melee damage in general upgrade, then increased damage based on each enemy you research, and some I won't spoil. After a certain point I stopped using my other weapons. In fact the only time I used my weapons was when I needed to do research, and only because "mixing it up" gives you more research points.