A game unfairly viewed as a follower rather than taking it's own path.
As the first Shooter outing of the Warhammer 40K universe/franchise it is easy to claim Space Marine follows the paths laid out by other Shooter franchises. However this is an unfair view as Space Marine is its own game, with its own strengths and weaknesses.
It's greatest strength, and simultaneously it's greatest weakness, is its usage of the established Warhammer 40K mythos with loads of references but never any lengthy exposition.
Anyone who's familiar with 40K will grasp pretty much all the references and feel pleasantly immersed in the universe.
Those who aren't however may feel a little bewildered by the broad universe and so not get the whole experience.
For example I felt the Orks were perfectly in character and acted as a different kind of antagonist to the Forces of Chaos who appear later on, those who aren't as familiar with the universe may find the Orks stupid and simple and not that different to Chaos.
While I think a method to bridge the gap in understanding is needed I'm not sure how it could be done in a way that doesn't slow the story down, perhaps an expanded Servo Skulls set up might have worked.
Movement wise the Space Marines, and the Traitor Chaos Space Marines in Multi-Player, have a distinct feel from many other Shooter protagonists.
The lumbering walk or jog of a Space Marine across the ground in their bulky heavy armour comes across on screen, as well as through sound and the vibrations of the controller.
The seeming inability of a Space Marine to navigate their often debris filled environment by climbing, ducking or jumping even small piles of debris can lead to moments of frustration when attempting to explore or get out of tight corners (especially in combat situations). Not to mention it seems like a rather glaring flaw for the 'Ultimate Champions of Man' to have.
Thus when you do get a jump pack it feels wonderfully liberating, though occasionally fiddly. However the jump pack is doled out far too infrequently within the Single Player campaign and for far too short a periods of time, though this is thankfully not an issue in Multi-Player - provided you pick the class which comes equipped with one.
While not as varied as some other shooter and action games the arsenal still provides enough variability in both hand to hand weapons and ranged ones to cater to different play-styles. It also feels less restrictive than some arsenals given in addition to your four guns you can have a small stock of grenades and your chosen melee weapon on hand. A nice touch is that in places you may have to alter your style a bit, though this is usually a case of having to abandon 'hack and slash' for a heavier focus on ranged combat rather than having to get into 'hack and slash' if you've been hanging back.
Now while the weapon selection/switch set up is similar to GoW and many weapons will feel familiar it seems only fair to point out that: there are only a few ways to switch between a large arsenal and naturally futuristic sci-fi shooters will come up with broadly similar weapons (ie charged plasma).
Combat is the place where Space Marine stands out the most from its fellows. While the recharging energy shield integrated into power armour many of us are so familiar with from other shooters is indeed present the game encourages you to take the fight to your enemy. The 'Champions of Man' don't cower behind walls and neither do you - Executions and Fury Mode are your health packs. While you can't abandon the concept of cover completely, along with the typical waiting for shields to recharge, it encourages you to get into the action a bit more than other shooters.
Having an actual melee aspect to compliment your arsenal of weapons, as opposed to the usual weak melee attack (punch/stab), melee weapon attached to weapon or hit-with-weapon provides a noticeable difference from other games.
Granted this is a hybrid melee-shooter game and so tries to balance these elements more than straight up shooters do, but even so the fact that you can actually get into hand to hand combat with most foes rather than having to keep your distance from all but the weakest foes is very nice.
The boss and mini-boss battles were definitely different from each other. I have to say the first battle though isn't terribly well conceived and can be more luck based than skill based even on easy but the others were all fairly clear and rewarding to accomplish.
The universe is very faithful to its source and overall 'dark, old future' genre with its grand Gothic appearance built long ago now thoroughly run down by time and being lived in, not to mention fought in a thousand times over.
The sense of scale in the story is also impressive as you're constantly aware the whole planet, not just your section, is a warzone - which only serves to make your role all the more pivotal.
In terms of the story and characters I feel again that people who know 40K will get the most out of this. The story is fairly solid and about as much as you'll get from a lot of games these days, in my opinion, moving at a steady rate and giving you both context and a reason to continue. Some characters may seem terribly limited and one-dimensional, but if you know the universe then subtle layers are added to them, still I think they're on par with at least some other characters you'll find in video games or other fiction.
In both cases, arguably as with other games, people who know 40K will get the most from the story and characters but neither element is weakened heavily by a lack of knowledge of the source material. They are very true to their source material to the point I'd argue any similarities you see are more likely the result of cultural stereo/arch-types rather than any copying of other franchises.
While it might feel similar to other games Space Marine walks its own path, complete with its own strengths and weaknesses. 7.5 out of 10 if you're not into 40K, 8.5 if you are – so it gets a happy medium of 8 out of 10 in my book.