In case the bloodied aparition on the box isn't obvious enough I'll reiterate that Manhunt is a game for adults only. Whereas some games take liberties with the intensity of violence on show, basically just adding extra crimson to their colourful spectacle, Manhunt's violence is dead serious and almost always bordering on unwatchable.
If you like your games with more wallpaper and less brain matter on the walls, no amount of praise is going to convince you that Manhunt is worth your time. However, look past the novelty extreme gore and you will find a solid stealth thriller.

Manhunt has you playing as a convicted felon who is saved from lethal injection by a snuff film producer/director. This director then places your character (James Earl Cash) into various run-down areas filled with gang thugs and films Cash's attempts at survival for the entertainment of his clients. The action is viewed from a Tomb Raider/GTA viewpoint and gameplay consists of sneaking from cover to cover, shadow to shadow, and dispatching the thugs in various twisted ways. Once you are in position behind an enemy that hasn't detected you you can perform an execution using the weapon you are holding. Hold the attack button longer and your execution will be more violent but you also leave yourself vulnerable to detection by a different enemy for longer. There are three degrees of brutality to these executions and ironically I sometimes found the 'medium' ones more horrifying than the extreme. How bad can "suffocation by plastic bag" get? How about a few cringe-inducing punches to the face, or an added neck snap? No need to expand on the baseball bat options - I think you get the idea.
The sounds that accompany these executions are realistic and have that proper quality to them that makes them amplify the violence onscreen. Crack, splat, thud. Basic sounds, but if you saw what was happening... Likewise the voice acting is excellent, apart from the various comments your enemies make you'll also have the pleasure of hearing Brian Cox as your sadistic puppetmaster.

Mostly Manhunt consists of waiting in the shadows and stalking your prey methodically, killing enemies one by one and sometimes dragging their bodies back into the dark with you. Despite having a level's-worth of hunters after you you'll interestingly enough soon get the feeling that you are in fact the hunter as you crouch in corners and wait for the moment to strike. In a way the game resembles a horror movie with you playing the killer. Since all your victims are murderers and rapists the violence inflicted upon them is easier to stomach.
Every few levels the scenery and thugs will change but the environments remain derelict, abandoned and threatening. It's hard to imagine a zoo feeling sinister but Manhunt's pulls it off. Just take away all the colour and add filth and murderers. Indeed, it's the levels and enemies that will keep you entertained, as the action does tend to get repetitive. Each gang has their own story and dress-style and all they're all suitably menacing.

Manhunt's gameplay limitations are its weak point, though. For one, while it's understandable from a design point of view, the choice to allow only one weapon 'type' to be carried at a time leads to some backtracking. I understand Cash doesn't have a toolbelt so carring hammers and crowbars might be complicated, but I would think he could fit a plastic bag and a shard of glass into his pockets... Also the game tends to focus more on firepower as the levels progress, not leaving you with many places to hide and placing you against difficult odds. This wouldn't be a problem, but Manhunt has unfortunately caught that disease of consoles, save points. In the easier parts it's not that annoying but at the end of the game it's really more an artificial game length extender than a welcome challenge. There was one area where a key I needed was guarded by a gang of 3 or 4 thugs inside a room. The only way into the room was through the door, which they were all staring at. I had to try to keep peeking in from different angles to try to get shots off at them and would frequently get killed and be forced to restart from earlier in the level. No amount of stealth would help me get past it. Manhunt features an array of such areas that are unfortunately usually near the end of save points, causing you to replay areas that may not have been that interesting in the first place.
Unfortunately there isn't much storyline in Manhunt. There is enough to keep you motivated but certain elements are left strangely unexplained. The first few levels will also have you just transplanted from setting to setting - it's a good excuse to let the designers add any area they wish, as it's the director who is doing the choosing - but soon there will be a method to the madness.

Manhunt has good graphics, excellent sounds and enough exciting missions to hook you. Whether you consider the extreme violence a perk or a hinderance is up to your preferences but you may be missing out on a challenging game if you let Manhunt pass you by. Alas you may not be the only one, as Manhunt's content makes it hard to recommend to anyone but the most mature gamers. If you do take the plunge, get ready for some gritty, gory thrills. Just please remember it's just a game.