Contains some minor spoilers!!
Everybody knows what isekai is: a guy dies and gets reincarnated in another world. Personally, I find that concept very fun and interesting. Even though it's hard to find a good isekai that doesn't fall victim to lazy writing, I always find myself giving isekai titles the benefit of the doubt. I wish I didn't in this case...
Jaryuu Tensei is about a guy that dies and gets reincarnated as a monster, a DRAGON more specifically. Now, how cool does that sound? Well, you'd think it would be easy enough not to fuck up when your protagonist is a fucking dragon, but everything with this manga is just so wrong. Let's dive in!
From the first couple of chapters you might think, "hey this might be an ok story", the MC is overpowered as fuck, yes, but his cute slime lackeys give you the hope that the story won't go the "I'll be an adventurer!" or "I'll build a city for monsters" route like other titles, since our MC apparently just doesn't give a crap about any of that... Until he swallows an orb and obtains a human form... That's where it all goes downhill to the cliché route of every isekai manga ever made. He gets a hot elf companion, starts doing jobs for the guild, kills monsters that no one else can etc. typical isekai bullshit.
Oh god, the art... The art is so bad, so unfit, and so comical, that it's impossible to take seriously anything that happens in this manga. Even the moments where people are brutally killed and butchered are hilarious and ineffective because of the utterly terrible art. I've seen better-drawn art by amateur artists on tumblr, and the only reason I'm not giving this a dogshit score of 1, is because at least it's better than anything I'll ever draw in my life.
Rushed is the only word I can think of that is appropriate for the characters in this manga, they're just never given enough time to be properly fleshed. 15 chapters in an isekai manga and the main character has no clear goal or motivation. He's just a carbon cutout of every other isekai protagonist ever.
Enjoyment? Forget about "enjoyment", this manga isn't even enough to scratch the isekai itch.
I wouldn't recommend it to anyone that doesn't want to purposefully waste their time. Go read Goblin Slayer, Saihate no Paladin, or Tate no Yuusha. They are much better titles that at least have some effort put into them.