If I use the Quickened Spell Metamagic to quicken a leveled spell am I able to cast a different leveled spell with my action, or am I only able to cast a cantrip/unarmed strike/throw something with my action?

If you cast a spell as a bonus action, the only other spell you can cast on the same turn is a cantrip with a casting time of 1 action.  So, in the case of using Quickened spell to cast a leveled spell as a bonus action you are *not* able to cast leveled spell with your action.

Thank you! That's what I thought it was, but I wasn't 100% sure. It would really help new players (i.e. me) if that were to be written in to the description of the Quickened Spell augmentation. Maybe that'll happen in an FAQ or errata sometime soon.

They try not to repeat themselves in the rules - and it's already written in the Spellcasting rules. https://www.dndbeyond.com/sources/basic-rules/spellcasting#BonusAction

If you're playing a spellcaster then you really should read the spellcasting rules anyway - because the bonus action rule doesn't just apply to Quickened Metamagic - it applies to all bonus action spells like Misty Step.