Well the prequel movies of course were going to be HUGELY difficult. They had piles of what seemed to be nearly impossible things to overcome.
The fighting scenes were old in the old movies, how to modernize them in today's over the top action, without breaking the story line. Of course the lack of training for Luke, and Vaders injuries made the perfect cover there.
The technology would be another, why are they wearing and using equipment that we already have improved upon in those originals, and how do you take that backwards? Well the beaten down worlds showing technology mostly at a stand still (Millenium Falcon is old but still can compete with modern tech for example), the "far far away" where equipment can be futuristic in some area's but behind in others, and the retro look (ships esp), helped out here. So many things were put in because they look great on film but don't make sense from a realistic point of view (death Star for example).
Beyond that, I was ok with the first chapter, but it wasn't great, nor did it meet my expectations. Worth watching, sure, worth re-watching again and again, not really. Seemed to be the most kid friendly movie of them all, even over ep 5's ewoks (which I think I remember hearing were only used because casting a wookie planet was too hard). There's always been humor (espec with the two droids), and I think the Gungans just seemed a bit too forced to make it more kid friendly and commercially successful. I understand the need to show the backstory, but maybe they could have done the first 1/4 of the story of young Anakin and bumped it up 10 years for the rest of that one.
2nd was better, had to push the love story, and maybe went a bit more into that than needed. 3rd I think finally went back to the action never ends feeling of the first few and is one of my favorites of the entire series.
I'm not a stickler for who said what when, who shot first, what slight hue change happened with who's lightsaber, or distance vs. time in parsecs (though the han solo books worked to correct that). No sci fi movie has a perfect story line without any plot impossibilities or questions, but for one as wide spanning as Star Wars, they do a great job overall (outside of the Christmas special lol).