Each to their own I suppose. I was absolutely riveted for the entire movie. I found the characters engaging; at no point did I feel the film was sagging or lacked punch. It was entertaining, it was traumatic. That scene where Cassian is manipulating the grabbers to search for the plans I could feel the skin crawling up the back of my neck. Even though I KNEW they would find them I was still thinking to myself, "the stormtroopers could be through that fecking door any second".
I knew far in advance what the cost of this mission would be, but I was still captivated by it. I suspended my disbelief and I can't wait to see it again.
I mean Vader... fucking Vader at the end. The most badass, exciting and harrowing thing I've ever seen in a Star Wars film. He's pissed, yet he's toying with them. He could have sent the stormtroopers in, but he wants the exercise. He's just a fucking machine.
Vader probably sends the troopers in at the start of ANH deliberately; he could do it himself, but he would probably have killed everybody in his anger, and he needs prisoners to interrogate. Easier to send a horde of stormtroopers in, 'cause their aim is so bad there'll almost certainly be somebody left alive.