Don't get me wrong, I despised the senate scenes in TPM. The story came to a complete halt when they happened. It was basically Lucas shouting LOOK AT THIS SCENE THIS IS IMPORTANT HISTORY LESSON. They really could have been massively trimmed.
The senate scenes were an example of poor scripting hurting an important moment that sets the stage for the rest of the series--it was that important. Palpatine's orchestrated chaos begins there--not the man sneering and the lightsaber fights obsessed over by the extreme SW geeks.
There wasn't any part of that romance that was even remotely credible. I almost would have preferred if we never saw any of it, and it was only revealed at the end that they had been secretly hooking up and Padme was now pregnant with the twins.
Instead of trying to turn it into some "epic, tragic romance" that just didn't work at all.
For the original films, Lucas took many sources of inspiration for the basic story, but in the prequels he was over the top, hitting audiences over the head in "sourcing" classical stories, all to sell the stillborn idea of Anakin being some kind, loving hero who falls from grace.
The problem in that is in order for Anakin to turn in the "teh worstest evil EVAH," it could not be believable to have that happen overnight, so almost from the start, Anakin had to be a self-obsessed, violent asshole, and that personality cannot stand side by side with some great, likable hero, and there's no Sith manipulation that would warrant an overnight change, anyway.
Then, there's the amateur show romance, which--as you said--just did not work at all. Padme's motivations were expressed like Lucas did not know how any woman thinks/feels at all. Moreover, aside from Portman's being cast in the series at a time when she was sick eye-candy for loser men still thinking about her role in The Professional, her so-called abilities left much to be desired. Whether it was the horrible "regal" queen voice, or her other whining voice, Portman added nothing to the prequels.
Well, I guess scenes of her in outfits or the bun hairdo meant to evoke memories of Leia made it all worthwhile.
Padme's hair went kind of overboard, in my opinion.
The Senate scenes could have been interesting, especially if there was far more political dealing that I think Lucas was trying to emulate from things like Dune. But, as it was, it felt like it dragged the story to a halt.
Also, the romance never convinced me that they loved each other in the way that they behaved. I guess I get what Lucas was trying for, but it didn't land for me.
As for Anakin's change to evil, it didn't work either. I mean, at least in creating him to be someone who I don't want to see fall to the Dark Side. Or even someone who is like Macbeth who ends up becoming evil despite initial success. The idea of hubris featured in Greek tragedy and Anakin's fall came about because he became so powerful that no one else knows what to do.
Something like that.