Having 2 party members isn't that big of a deal, but they needed to open up all 6 classes from the get go. That was the main problem as far as combat goes.
XIII would benefit tremendously from an in depth remaster like The Zodiac Age where they actually go in and change things. Add side quests, mini games, and NPC interactions that eliminate the need for the data log and help break up the battle/cutscene/battle/cutscene nature of the first half of the game, open up all 6 classes from the get go, overhaul the weapon upgrade system so you know exactly how many resources to invest and know exactly what you're going to get from it, as it is right now you need a guide.
The combat, visuals, music, art style, and polish are all top tier, the game is so close to being amazing, i still love it despite its flaws though.