[1] The most distinguishable trait of harem works is the presence of a single protagonist surrounded by multiple different characters who are treated as options for a sexual or romantic relationship.
Many harem love interests are easily enamored with the self-insert; falling for the main character because of simple kindness or coincidence, often described as due to their low self-esteem.
[2] Harem works frequently put off commitment to any specific love interest for as long as possible, sometimes indefinitely; commonly executed by oblivious or easily-flustered protagonists.
Especially in dating sim visual novels, it has become increasingly common for harems to feature characters of multiple genders, with the player choosing whether to pursue an opposite- or same-sex relationship.
Critics have also argued that harem genre tropes around a passive protagonist effortlessly picking and choosing from multiple eager suitors furthers the mythos of men being entitled to female affection, and can lead impressionable male readers to react negatively to being rejected by women in real life.