A friend of mine expressed the same sentiment as you, get. He would've liked to see Maul in a continuing role beyond Episode I and was actually pissed when Obi-Wan killed him. I thought the storyline for Episode I was good in that it centered around the invasion of a planet, one that we've never seen before. It was dissapointing to find that Anakin was from the same frickin' planet as Luke (it was bad enough that we went back there in ROTJ), and while it was nice to see Coruscant, that too was a planet we'd already heard of and seen (in the ROTJ SE). And then what do they do? They go back to the same three planets again in Episode II! That's what frustrates me the most about that movie. Kamino and Geonosis were the only interesting parts. Luckily Episode III stayed the hell away from Tatooine and Naboo until the very end, and even then it was very brief. I think Lucas kept to his original plan for the PT but changed a whole bunch of things along the way. Intercutting a lightsaber duel with another lightsaber duel was a first for the saga, but again, too much coruscant. One defining thing about the OT was that the only location we saw in all three movies was the interior of the millenium falcon. In the PT it's like this entire galaxy far, far away is confined to the senate chamber and palpatine's office. What gives?
I remember hearing ideas for the movies, some of which I'm pretty sure were confirmed facts, that never ended up happening. Episode III in particular, Anakin was supposed to gradually collect pieces that would become his Vader armor. That didn't happen. "The duel" was supposed to go on for quite a while, and maybe it does, but the merits of intercutting it with the yoda/sidious duel is anyone's guess. Mustafar and Utapau were fun to see realized on film.