Bio Shock 2 is undoubtedly a great FPS with great graphics, enemies, weapons and story line BUT..... it's not as good as the original (in my opinion). For a start the original Bio Shock took me ages to complete presenting me with challenge after challenge but BS2 took me just a week or so and felt pretty straightforward or dare I say it... easy!!!!
Don't get me wrong I still recommend this game BUT if you don't already own BS1 then get that first - it's a better and more challenging game - then buy the sequel for a bit of 'follow up' fun!