"High school seniors" is a noun phrase that makes up the subject of the sentence. The simple subject is seniors and the compound adjective high school describes the type of seniors. "Will love" is the verb phrase. Love is an action verb because it is something you can do. Will is a helping verb that helps put love into the future tense. "The theater" is a direct object. It tells what the high school seniors will love. Direct objects receive the action from the subject.
