Lycanthropy is described in the Monster Manual as a curse. Some members of our party contracted it from a pack of werewolves in a recent session, and we consulted the infobox in the Monster Manual to see what effects it has.
The infobox “Player Characters as Lycanthropes” on Monster Manual page 207 states:
A character who becomes a lycanthrope retains his or her statistics except as specified by lycanthrope type. The character gains the lycanthrope’s speeds in nonhumanoid form, damage immunities, traits and actions that don’t involve equipment. …
… If the character embraces the curse, his or her alignment becomes the one defined by the lycanthrope. The DM is free to decide that a change in alignment places the character under DM control until the curse of lycanthropy is removed.
…
Werewolf. The character gains a Strength of 15 if his or her score isn’t already higher, and a +1 bonus to AC while in wolf or hybrid form (from natural armor). …
To me, this sounds like a very positive curse to have. A player who chooses to resist the curse gains a passive buff to Strength (unless their Strength is already 15 or more) and some very potent damage immunities. The alignment change and the associated loss of PC control is conditional on the PC embracing the curse, and as such it’s not really an issue. One can even remain in humanoid form to avoid socially awkward situations using the Shapechanger ability.
So, is there any mechanical reason to not contract lycanthropy, or a reason get rid of it after contracting it? What makes it a curse?
The infobox makes it seem that loss of character control only happens if the PC embraces the curse and the DM chooses to take control of the character, and therefore simply not embracing the curse would suffice to keep the character as a lycanthrope complete with powerful boons like damage immunities but without any drawbacks. However, the lore earlier in the lycanthrope chapter suggests that the condition is impossible to resist during full moon:
A lycanthrope can either resist its curse or embrace it. By resisting the curse, a lycanthrope retains its normal alignment and personality while in humanoid form. It lives its life as it always has, burying deep the bestial urges raging inside it. However, when the full moon rises, the curse becomes too strong to resist, transforming the individual into its beast form — or into a horrible hybrid form that combines animal and humanoid traits.
(from Monster Manual, page 206, under Curse of Lycanthropy)
Even a character that resists the curse is unable to control their bloodlust during full moon, as is traditional to werewolves in fiction. Ask your DM to keep track of the phase of the moon while you’re infected so you know how fast you need to get a remedy or other countermeasures.