: I think it's completely in keeping with the Didact's character and his
: attitude toward humanity in general. He's impressed by the Chief's
: tenacity, but he NEVER considered him a threat until he saw him running
: toward him with a Pulse Grenade.

What about when he saw the Chief running toward him with a nuke?

: He's a proud character.

Since when has pride been a synonym for 'stupid'?

OK. Let's think this through. The Didact isn't just a warrior, he's a general. He's commanded troops, led campaigns, fought against augmented humans.
And as you put it, he thinks that throwing a Spartan in power armor across a room is going to kill him.

The Didact is an idiot.

Or how about the rest of his approach to killing the Chief? You mentioned that the Didact was at least throwing Covenant and Prometheans at him. But he lured the Chief through an entire army of both in order to get himself released. And if he bothered to ask Jul to catch him up on current events, he'd know just what the Chief accomplished a few years ago.

: Granted that's a trope of most villains, but I think it's
: pretty justifiable here. The Chief's luck got him out of ridiculous
: situations plenty of times when Bungie was taking the reigns.

No, it's not justifiable. Like you said, it's a trope that's been used and abused to the point that it's a cliche.
Now, tropes aren't bad, and even cliches can be used to tell a good story. But when they're not used well, the audience is going to be comparing this story to the better ones they've read/watched/played. I call it the "Bad Coffee Effect".

Now for the Chief's luck.
I don't mind it being used to explain why he's a one-man-army, or how he can jump from a Dreadnought into an African jungle. But when it's being used to justify simian-level IQs, I've got better stories to enjoy.

: You're simplifying things too much, ain't ya? :P

No, no, that's pretty much what it boils down to.

: The Earth was in the middle of getting Composed when you reached the Didact
: and the Composer. The threat is literally staring you in the face.

Another Villain of the Week is firing a beam weapon at Earth.
Yawn.

You know why Halo: CE worked? Because we were on the ground. We saw what the Flood could do. We got hints that they could do something worse. We found out that the only thing worse than the Flood was the weapon that was built to contain them. And not only was the galaxy in danger, but we were too.

Halo 4 has none of that setup. Sure, those people were blasted, but what happened to them? Why was the Chief spared? What sorcery is this?

Oh, what was that? It was all explained in the terminals?
Sorry, but not only were those terminals painful to watch, but they required me to exit the game and go to Waypoint to watch them. That is not, by any stretch of the imagination, a good way to tell a story.

: And the
: ease in which they were destroyed? What about on the Ark in Halo 3? All
: the Chief had to do was stroll up, push a button, then watch the Arbiter
: stab a sick old man. Bam. Universal disaster averted.

After which you had to escape from the Flood after their sudden but inevitable betrayal, fight your way onto High Charity, and then blow Installation 04-2 up in order to stop the Gravemind. And if you even got that far, you had fought your way through the Covenant Schism.