What's so alluring about Tolkien's Lord of the Rings and The Hobbit?

I would argue it's down to story. What keeps us gripped here is, despite the film's epic length (an at points it is far too long, especially the ending of Return of the King), it is the inspiring courage and mystery that surrounds a small characters' journey into the unknown, vast, dark and often evil world. It conveys the sense of home as a value worth fighting for: I'll never forget Sam and Frodo's journey to Mount Doom in Return of the King, when Frodo faints near the entrance and Sam carrying him the rest of the way to the sound of spine tingling orchestral music as he reminds him of "Strawberries and Cream..."
The Hobbit, set before Lord of the Rings, does the same, except this time the Dwarves must recapture their homeland stolen by the Orcs and a Dragon under the evil plans of Sauron.
That's the reason we don't get bored with the incredibly long, complex narrative- we care about what the characters are fighting for, and the more they are prevented from achieving their goal, the more we want them to achieve it in one heroic, climactic swoop.

The most interesting character I find is Gollum. The way his character is torn between contradictions is masterful, and constantly keeps us guessing as to whether he will help the help Hobbits as Smeagel, or gain possession of the Ring as Gollum. The answer, of course, at the end of his character arc, is Gollum, but we feel a great sense of satisfaction from this curious creature's journey through his moral torment and tough decisions that lend his personality great depth.

Jan Svankmajer's ability to keep audiences Engaged

I'm not keen on surrealism, which is why I found much of Svankmajer's work slightly annoying in the way that it was far too random and unrelatable. This includes shorts like Dimensions of Dialogue, which despite keeping us guessing at how the textures in the animation were going to shift next, made very little, if any real sense.
What he is a master at, is his ability to keep the audience engaged, and his most genius example of this is Down to Cellar. This masterpiece in creating character empathy and POV centres around a little girl who walks down the stairs to collect potatoes out of the cellar. A simple story premise, powerfully engaging through tension and horror.
As the girl walks down the stairs, she passes the looming stares of a creepy old man who offers her a sweet and middle aged woman who gives her a sordid glare. A Cat screeches and stands guard at the gate of the cellar. The girl struggles to get light as she walks through the dark passage and hears strange whispering voices.
She encounters the old man lying on a charcoal bed ushering her over and the middle aged woman offering her a charcoal burger. As she runs away from this, and the cat follows her, screeching, things begin to get even more creepy: She tries to fill her basket with potatoes but they keep rolling back inside the box, and when she finally grabs hold of them and reaches the stairs of the cellar, the cat distracts her and the potatoes go scattering back into the cellar. We feel for her frustration, her disappointment that she must now undergo this ordeal once more...