This game is just plain fun. I have played over 40 hours so far and beyond an early bug where I couldn't finish a main storyline quest, it has been very smooth playing and very well done. I feel that I probably have at least that much more time to play, and probably over 100 hours total before I move on.
I have been focusing on side quests and NCPD tasks for the most part as making money early on really helps with upgrading your cybernetics and so on. A great wealth of guns, knives and armor to play with, and an incredibly large map to move through the city.
Some of the cutscenes are a bit too long, and the interlude after Act 1 while interesting really takes you out of the main story without any notice, but you get it once you go past that point.
Several really groundbreaking things for me - natural conversations with people around you, there is still a "talk button" but important conversations just start when you are close to that person. The map is well done, with various tasks, shops, fast travel points and so on clearly marked. You always have many things to do other than the main storyline.
Fights are fun, you realize quickly that just running around shooting people isn't smart, and some strategy is involved, especially early on. The stealth mechanics really work nicely and it seems that you get paid more for jobs that you complete without blowing everyone away as well.
Inventory management is well done, lots of various tabs that take some getting used to, but gives you a lot of control over your character and your items, leveling up, etc. I find between disassembling items, and selling them I never worry too much about weight. Make sure you hit up a sell point after fights though, the amount of stuff dropped or found is amazingly high.
My computer is brand new and high end, so I wouldn't expect any problems playing this game - older machines might have more of a problem, as it is graphically intensive.
Overall, tons of fun so far!