It’s fairly similar to the base investigator. You can cast buffs on your allies without having to take a talent. The poison abilities barely ever come up anyway and in its place you’re really good at identifying magic items, which can vary in usefulness depending on if your GM requires those checks to identify items.
It does swashtigator just as well as the base class so consider taking a level of inspired swashbuckler for a dexterity build.
You actually cast arcane spells so you can take arcane strike and feats that require that such as riving strike or spell cartridges. That doesn't mean that you should, but it is a difference that makes the Antiquarian unique among investigators.
Along the same lines you can actually craft magic items which most investigators can't. Also, you cast spells so you can use spell trigger and completion items. All good improvements.
Take a look at the Questioner, psychic detective, and jinwei archetypes if you want a different spell list but otherwise like the investigator chassis.