The finale of the Iron Man Trilogy demonstrated that just because the second film wasn't up to scratch doesn't mean the third has to follow suit. Iron Man 3 was a wholly different film than the previous films in the series; it wasn't a simple case of Stark's own technology being used against him while he tried to prove himself to Pepper Potts.
We're taken into the anxiety-filled world of a post-New York life, post-Avengers Assemble. Tony isn't capable of standing on his own two feet at the thought of the battle, at the thought of entering into the wormhole and damn-near dying. In the comic books, he doesn't experience such a cruel fate of heroism, at least not so early in the Avengers career. In the comics, he doesn't have to deal with the fact that he almost died so early on in his life. In the comics, instead of dealing with a severe anxiety problem, he suffers from alcoholism.
Stark's demons are at the core of Iron Man 3. We see a lot more of the man behind the mask in this instalment, much more than we've been given a chance to see the previous three films he's had an important role to play in.
As for the Mandarin... my experience with Iron Man as a child showed the Mandarin to be one of his most dangerous enemies. He also used magical rings. That's a bit of a stretch for Marvel with these films. Though Thor and Loki use magic - in a sense - no human has ever used it. So, we see the Mandarin leading the Ten Rings, a terrorists organisation. You might recognise them from the first film. They were the crowd that kidnapped Tony Stark, from whom he escaped using the first Iron Man armour. I always knew Marvel had a plan for these films, and that just proves it.
However, the Mandarin wasn't the only thing from the comic books that made its way on-screen. Extremis, a DNA-altering drug, shows up as a terrorist weapon. We don't have Mallen, the first person to be injected by it in the comic books, but we do have Eric Savin - Coldblood - to take his place. He's a violent one, the lead henchman, and provides more than enough trouble for Stark...and the US government. Extremis was used well within the film, creating a real sense of danger for innocent people, and creating a situation that made victory difficult for the troubled Stark.
MAJOR SPOILER ALERT
My one big question though, is how do they intend on bringing in Tony Stark into Avengers 2? A simple case of heart surgery changes everything. He's no longer attached to an electro-magnetic-ARC-reactor. He's no longer his armour. He's no longer Iron Man. And he blew everything up.
Where the hell do they go from there? Yes, it was the ultimate sign of his redemption, his ultimate transformation from self-obsessed billionaire to Regular Guy in a Relationship billionaire, his way of finally dealing with his anxiety issues, his complications, his troubles. But it separates him from Bruce Banner, the other hero who is his armour, like it or not.
With only rumours as to who will join the cast in Avengers 2, though a confirmation that we'll see the Scarlett Witch and Quicksilver (!), it's hard to tell where they plan on going. Even with the notice after the credits that Tony Stark will return, can we confirm that he'll be an Avenger? Only time will tell, and there's plenty of it before we even complete the four announced films that make up Phase 2 (Iron Man 3, Thor: The Dark World, Captain America: The Winter Soldier and Guardians of the Galaxy). Still plenty of time for Marvel to sign new contracts with the actors, right?