At a rough guess, I think I’ve put around 18 hours into this. My understanding is you can complete it in under 10, but since I have OCD, I had to search everywhere, examine everything, access every bit of the map, open every door, hack every machine, rescue every Little Sister, max out every research track, buy every plasmid and gene tonic slot, and listen to every audio diary. I even found myself using up ammo just so I could collect more ammo to replace it. Yes, I clearly have a problem.
How to sum up the game without spoilers? Well, it was more of the same of the first game really. Some improvements (dual-wielding plasmids and weapons, better “where am I going” hints, less getting lost), and some let downs (more linear game, too many “collect X of Y”, less powerful storyline, no proper end boss). Still an excellent game, but perhaps a 4/5 rather than the 5/5 of the original.
Strangely, the thing I missed most from the original was something I thought quite irritating at the time – all the vending machines singing “Welcome to the Circus of Values!” and stuff whenever you went near them. They rarely did it in the sequel.