The ending of Iron Man 2 resolves Tony's health, leaves Rhodey in a military suit, and quietly turns Tony from a lone hero into someone who works alongside S.H.I.E.L.D.
Vanko's attack ends when his armor and drones are destroyed, and Hammer is arrested. Tony and Rhodey are given medals, and Tony ends up as a consultant to S.H.I.E.L.D. rather than a full member. Rhodey keeps a military armor as War Machine.
In my opinion, the consultant detail is the most important beat of the ending. Tony spends the film refusing to hand over his technology, and the compromise is that he keeps his freedom while joining a larger structure on his own terms. It could be argued that this is the film's real answer to its opening question about who owns the armor.
The cure matters too. Tony does not fix himself with a new gadget alone. He builds a new element from a clue his father left, which ties the personal story to the Stark family and to Howard Stark (John Slattery) in particular. Perhaps that is why the film feels more like a family inheritance story than a repeat of the first movie.
The medal scene also reads differently against its neighbors. In Iron Man (2008), Tony's big moment is announcing that he is Iron Man, a solo act of ego. Here the public moment is a shared one, with Tony and Rhodey (now played by Don Cheadle rather than Terrence Howard) honored side by side. The Vanko fight at the Stark Expo is also a two person set piece, with Natasha helping, which is a small rehearsal for the team fights of The Avengers (2012).
The Natalie Rushman reveal is the other hinge. Nick Fury tells Tony that his assistant is the S.H.I.E.L.D. agent Natasha Romanoff, and Scarlett Johansson then plays her in The Avengers (2012). Compare that with The Incredible Hulk, released between the two Iron Man films, which links to the wider universe more lightly. Iron Man 2 is where the connective tissue becomes the plot.
Finally, the film sets up the wider team-up story that leads toward The Avengers (2012). If you need one reason to watch this film before that crossover, the reveal about Natasha is it.