Even though the question has been resolved, even IF space marines all looked alike feature wise, if you watch Star Wars the Clone Wars animated series, it does an excellent job of showing how the clones are each unique, and no that is not an oxymoron. While they all have the same baseline, they paint their armours in unique ways, develop names, and each show their own distinct personality. Excellent work from the voice actor, by the way.
I suggest anyone that is being apprehensive to the Deathwatch game, watch the Clone Wars and imagine the clones as Space Marines.
Also for another analogy, you could almost imagine the battledroids, and how Grievous treats them as the Imperial Guard, and a Commisar respectively.