A really neat science fiction game that still falls short of the original.
Level design has changed a bit, with smaller, more compact maps that bring players into closer proximity with their enemies than in the first game. It has been my experience that this tends to limit the practical choice of weapons throughout gameplay.
Speaking of weapons, there are upgrades that can be performed to expand their usability and effectiveness, just like in the original Deus Ex. But whereas in the original game kick, reload time, magazine capacity, range, accuracy, and other factors could be improved upon, the new game primarily tends to focus the mods on giving weapons unique, new, James Bond-like capabilities. For hardcore fans of the original game, this might feel a bit contrived and unrealistic, such as the option to have your weapon disintegrate glass silently or have a bullet do EMP damage. It does make gameplay more interesting, but I found myself missing the ability to systematically enhance your preferred weapon of choice into a more dangerous and lethal instrument.
Ammo too seems to have been overlooked. In the original game each weapon had its unique ammo. In Invisible War, there is a certain nanotech ammo that conforms to different calibres and weapons. In accordance with the nanotech atmosphere that is pervasive in both the storyline and atmosphere, this is appropriate, but it seems to be less realistic or credible.
Ostensibly related to the refined game dynamics and a move towards being a truer FPS, Invisible War has also dropped certain other elements of the original game that might have seemed too extraneous. The leveling system of the original, where players could improve their skills with different weapons, computers, swimming, etc, is a thing of the past.
The storyline is a separate area for debate. I have a feeling most people will be quite satisfied with the plot, as it expounds upon a globalized world network with several dissident political, religious, and science-based factions. It takes place two decades after Deus Ex and features all the conspiracy and political philosophy present in the first game, though at times it seems much more morally ambivalent, with several choices of contradicting quests, none of which seem to be anything short of seedy and unethical. There seems to be less freedom to use your own judgment if you wish to uphold justice or attempt to do the right thing. No matter what group you choose to assist, you will find yourself performing questionable assassinations and subversive actions. On a separate note, though, there are several different possible outcomes to view, giving the game good replay value.
In the end, if you can enjoy this game as a cyberpunk FPS with elements of RPG, and just have fun seeing the different possible outcomes, Deus Ex: Invisible War has the capacity to provide many hours of enjoyable gameplay. I do hope, however, that Deus Ex: 3 will be an FPS-style RPG like the original, not an RPG-style FPS.