People often underestimate or under-appreciate the ability to produce a genuinely good B-movie. There's Renny Harlin on one end of the spectrum, making crap like The Legend of Hercules, 12 Rounds, and The Covenant. But then you have someone like Jaume Collet-Serra, who knows a thing or two about framing a scene, getting good performances from his actors, and above all, making an entertaining movie.
The Shallows could have been an otherwise conventional and forgettable thriller without Collet-Serra's strong and stylish direction. For example, the scene when Blake Lively's character first gets attacked by the shark is beautifully composed - in one unbroken take, no less - and legitimately nightmarish, with the red blood slowly overtaking the blue screen. It also doesn't hurt that Lively successfully carries the entire film on her shoulders, giving what is arguably the best performance in her career to date. There's a quiet fierceness and admirability to her character that makes it easy to root for her survival.
Overall, there's a lot to like about The Shallows. It's gorgeously shot, suspenseful, emotionally gratifying, and entirely successful on what it sets out to be - a solid B-movie, and it takes skill to pull that off. Sure, it doesn't match the heights of either Gravity or The Martian, but then again, its budget is a mere fraction of what those films cost.
