I'm just gonna copypaste something I wrote in an old rec thread. Some good series with monster boys with a lot of content/fanart and whatnot + entry points.
Nocturne seems to be the most common entry point into mainline and recently came out with a remaster. There's a bunch of different spinoffs like Digital Devil Saga (more character driven), Devil Summoner, and Devil Survivor (srpg). Strange Journey is a dungeon crawler. The mobile game, Dx2, is actually pretty decent gameplay-wise for gachashit.
Anime-wise, Adventure and Tamers are widely considered the best, Savers if you want more, Appmon is divisive, Xros Wars sucks don't bother. New anime called Ghost Game is coming soon. Game-wise, "World" games tend to be monster raising sims and "Story" games are typical JRPGs with a couple exceptions. Cyber Sleuth is the most recent game and widely available including on Steam. ReArise is a mobile game and decent for what it is. There's also various manga of various quality if you want more out of the franchise.
A lot of people start with the 2nd game and then go into 3. The anime is hilarious and recommended if you want some comedy. The Shadowside anime and Forever Friends movie are a more dark take on the franchise, along with the 4th game which unfortunately hasn't been translated yet. The movies are stand alone and actually pretty good. There's a few spin offs, namely Busters and the sentai-esque Y Academy. The mobile game Puni Puni isn't the best but it's there, there's also Sangokushi: Kunitori Wars. There's undubs of the games floating around if you have a hacked 3DS.
Mobile game. It's better than most gachashit, but in the end is still gachashit so keep that in mind. Try it if you like Japanese mythology.