Episode 1's main problem (beyond the awful dialogue, shaky pacing, and generally low-stakes plot) is that it's completely unnecessary in the greater storyline.
The movie introduces 3 "major" characters who had, before this film, had never been referenced in the original trilogy -- Qui Gon Jinn, Darth Maul, and Jar Jar Binks -- and then proceeds to kill off two of them. The third, Jar Jar, becomes a background character for the remainder of the trilogy.
They could just as easily have started the trilogy with Episode 2 and have the entire thing make just as much sense. Doing that actually makes MORE sense, because it starts Anakin out (for the viewers) at roughly the same age you meet Luke in "A New Hope" -- then the two trilogies become mirrors of one another with the contrast of choices between Anakin Skywalker (turning to the Dark Side) and Luke Skywalker (resisting the temptation and remaining true) that ultimately leads to both their salvations.
You also don't have to go through mental gymnastics to make the Anakin / Padme romance make sense chronologically, and you immediately start with real action as opposed to a low-stakes conflict about a trade dispute and blockade around an otherwise unimportant planet. It also ties in better with the dialogue in the original trilogy (Obi Wan's statement about Anakin being a great star pilot when he met him -- really, a 7 year old kid? Come on.).
The other main problem is that they did just a terrible job of explaining why Anakin fell. The whole character arc seems tremendously unsatisfying because, again, the spend an entire movie with him as a useless kid where you never get a sense of who/what he is or what makes him tick. If you start with Episode 2, you can do an entire movie of him being a generally affable dude and buddies with Obi Wan before doing something to him that starts the process of his turning.