Yiffalicious is a sex simulator... a sex animation tool? A sex poser toy? Whatever it is, it's a program where you place characters in lewd situations and basically build sex scenes using a simple-ish system, involving a lot of simple concepts like penetration depth and speed. The whole thing is easy to use and easy to fap to if you are into furries, and especially if you like cum inflation.
The first thing you'll notice is that you can definitely feel how unfinished this game is (I'm glad they decided to toss it and make a sequel).
Character models vary wildly in quality, as does the worlds you can place characters in, and infamously one of the worlds is exceedingly poorly optimized compared to the others.
As the content is entirely user-submitted, the actual sex scenes themselves vary terribly. Some good, most bad. Some submitted scenes are complex, with characters in creative poses and swapping between different speeds and depths realistically, while some submissions are, well, two characters just standing there because the goober uploaded something long before they actually got anywhere in making the scene.
Overall I'd recommend trying the game at least once if you're into furries and sex, but honestly you're not going to play too long, as the editor doesn't really allow much more than sticking peens in things (not the mouth) and adjusting the speed and thrusting and such, characters can't, say, flip the receiver around and swap to anal mid-sex, etc.