I like what the designers are doing with this new "half-caster" mechanic. While 4 spells PER DAY is certainly limiting, being able to cast up to 9th level spells is huge. One of the biggest downsides seems to be the lack of low-level utility... For example, if you were a 13th-level magus, when you're able to cast 6th and 7th level spells grabbing staple utility spells like Invisibility, Mirror Image, Dimension Door are going to be VERY costly, considering you are going to be giving up a 6th or 7th level slot for maybe a 4th level spell??? It just seems like no player in practice is going to make that trade off.
However, the designers added the "Martial Caster" level 6 feat to address this. Basically, adding an extra 2 slots per day to prepare mainly movement oriented utility spells. I think it would really add to the versatility and customization of the class if there were more feats like this available. Maybe an Illusion focused one that adds Invisibility, Mirror Image, Illusory Disguise etc..