I think the dialogue between Han, Leia, Chewie and Threepio, while trapped in the MF and on the run from most of the Imperial starfleet, is excellent.
I really think you're unfair to the writing of Leia's character. She's just been fighting to defend the rebel base on Hoth when she's forced to run, against her will. She gets trapped with Han and has to leave with him, bearing in mind how they've been getting on in the film so far. Not only that, but she has to share the ship with not just a chauvenist, but a big hairy animal and a prissy, cowardly motormouth as well. Add to this that they get further and further separated from the rest of the rebels in a ship that's falling apart around their ears and then wander into an asteroid field. After that, she's taken to meet the chauvenist's friend, who turns out to be a slimy charmer who's eyeing her up. Then it turns out that they've walked into a trap and they're bait for the nice guy, who she likes.
Considering that all she wants to do is get back with the rebels and get on with things, I think she holds it together pretty well.
Of course, all this is compounded by the fact that she is confused and very irritated by the fact that, despite all the things she hates about the chauvenist, she finds him irresistably attractive. This pisses her off no end.
Therein, I feel, lies ESB's greatest asset, in watching Princess Leia and Han Solo fall in love, despite themselves.