Great gameplay , graphics, story, variety, characters, and a huge universes to save or take advantage of.
You get to characterize your own character. The game also has great graphics and amazing environments; natural and futuristic. The ability to travel across the galaxy using mass relays was a good experience. Being able to jump from one habitable galaxy to the next gave you that Star Trek feel.
The combined real time shooting combined with the strategic uses of your character and your squads special abilities added variety to the combat. The abilities ranged from weapon power ups to psi powers.
The story was great. Humans have just been accepted to the galactic alliance of advanced species. A guy who hates humans and wishes to put them back in their place poses a threat to all sentient life in the galaxy by allying himself with an ancient machine race. You have to trek the galaxy and look for any clues or information that will bring you closer to this threat.
The graphics of the game were amazing. The character models and their armor were very detailed and crisp. The facial expressions and body language was very believable. The environments were very detailed. There were post apocalyptic and lush green environments the were void of life and rich with it, respectively.
Overall, the game kept me hooked in with its action and story.