The difficulty: challenges and tasks are on par with more known games. It pulls you in for multiple hours of play. Bosses will likely need multiple attempts to defeat until you learn the tricks to beating each. Classically like many games within the genre: game starts off with a sense of progression, and then you get submarine, and better weapons, allowing you to move more about the game to separate areas and complete tasks or just gather supplies.
Negatives despite the quality of game, the graphics lacked and appear dated, controls may work well but were hampered by waiting for video to play out last moves. To that, too many wait and watch scenes to play out. Storyline was good, but not entirely understood, but after an attempt on the final boss one must watch game credits before re-attempts, forcing this user to force close the game to play from the last saved location, which coincidently is the same location if you wait out the credits. Final boss win is anti-climatic, dude disappears and video plays of parting ways of robot assistant, (who, BTW, just pushed you into the boss fight, changing the storyline completely), then credits again.
I'd recommend the game, because of the brain work and challenges, with the caveat that the anti-climatic ending, poor graphics, and lack of scene skipping may cause loss of interest, frustration, and putting away for some time. It's beatable, takes mild-moderate effort, with multiple re-attempts.