Superficially Watch_Dogs resembles many other third-person shooters without fixed camera angle, although it does have a fixed zoom level. The majority of the gameplay is split between your typical explore/run/gun model in third person view and driving in one of a modest range of vehicles.
First off, we should mention the one save per retail copy problem. Watch_Dogs makes use of an automatic saving system that updates on game progress with no direct input from the player, and only one game profile is available per account. We can accept the lack of quick-save/quick-load to improve immersion but to not support additional profiles is very disappointing, even after noting that (real-world) smartphone integration could make this potentially difficult. We're not sure what the process is like on console but this should be a major stumbling block for multi-gamer households. Frankly there's no real excuse for this in a PC title, whether or not there is little consequence to your in-game decisions.
We should additionally note that by default large amounts of mouse acceleration is incorporated into the standard Keyboard/Mouse control system. Although this can be diminished by reducing X and Y-axis sensitivity there doesn't appear to be a means of eliminating it entirely using only in-game options. Hopefully Ubisoft will provide a means of patching it out.
As you explore the Windy City it swiftly becomes clear that whilst it has an open world feel the narrative progression is anything but; there are no branching stories, multiple-objective tasks that can be completed out-of-order, or even ways to redo specific missions within the main campaign. Still, while in-game maps direct you between missions as well as highlighting points of interest using a waypoint system, you are free to roam anywhere on the map without loading screens and engage in side-quests or mini-games at leisure.
The in-game map has all sorts of points of interest
In the course of your gameplay you'll also uncover side-missions, generally by hacking the phones of persons of interest. These quests, most often called 'Fixer Contracts', have you perform a task such as waylaying a criminal convoy or hunting down a getaway car for cash and experience. There's no time limit on Fixer Contracts, nor most of the offbeat activities you can partake outside of the main campaign, and many will persist between gameplay sessions.
Activating a mission or contract will zero the game world, despawning any cars you were using and spawning all the items you need to complete the mission. Reloading from death spawns you at your most recent mission completion point, also respawning any mission-critical doodads along the way rather than keeping track of the exact state the game was in at that time. The feeling that you make little impact on the world is therefore reinforced quite heavily.
Travel through Chicago can be performed on foot, in a vehicle, or via unlockable fast travel locations. The latter should probably be discouraged unless you are time-limited as it drastically reduces the chance of random missions spawning.
Enemies and Overall Difficulty
Watch_Dogs is essentially grounded in realism and so keeps the range of enemy NPCs to a minimum. Gunplay typically pits you against footmen with varying levels of armour, equipment and weaponry, whilst driving is generally more of a pursuit mode concluded on foot or evasion mode against increasingly fast vehicles. With the exception of heavily armoured Enforcers no enemy poses much of a problem unless you're caught in open ground, at which point you can be killed easily. Headshots are as always critical.
Missions are most often time consuming rather than difficult, the exception being criminal convoy missions which often demand precise driving that isn't easy using the default control scheme. 'Realistic' difficulty (one higher than 'hard) setting is genuinely tough due to the need to avoid gunfire if at all possible, but although higher difficulty levels pose a reasonable challenge defeating them doesn't feel any more satisfying than lower difficulties. Difficulty can be changed at any time via an in-game menu.
The challenge in Watch_Dogs will likely be in finishing the game through the use of stealth rather than force of arms, much like Deus Ex where stealth was more of a central theme. Unfortunately there appears to be little reward in going down this route.