If you know what Vore is you've already decided weather or not you like it, and if you're going to walk into this, you had better damn well like it because you're going to be seeing it a lot. That's all there is in fact, there aren't even pixel-art nipples (minus the lamia). I don't really like it myself but I was on a streak of sidescroller H-Games and decided to give it a go.
And holy fuck, if you're in this for the porn you're going to have to fight for it. If you're the type to complain about Dark Souls hitboxes this game is probably going to piss you off. As I said I'm not exactly a huge vore guy but this game is suprisingly a very competent beat 'em up, which is why i played it through to the end. Whoever designed this knew what they were doing with the controls. There are 4 characters, each of which have a pretty unique feel; there's a Valkyrie lady who has a laser sword/whip thing and can fly slightly, there's a catgirl brawler type who shoots fireballs and is seemingly DESIGNED to constantly get grabbed by enemies, there's a bunny girl who is literally just a Metal Slug character (probably the most well animated on purpose, though that's subjective), and an android who plays a lot like Mega Man. They each feel unique, and they each have a different level of complexity in their control schemes. Echidna Wars is honestly 90% game and 10% porn, at least in terms of complexity and the amount of what's on offer. Which is why, if you're not very good at beat 'em ups or video games in general, I'd suggest turning the difficulty down unless you want to turn your normal boner into an angry boner after getting grabbed for the five-hundredth time in a row. If you're up for the challenge though, there's plenty on offer.
As far as sex scenes, there's only Vore, and only fail conditions. Everything is "on-stage" so to speak, there aren't any CGs minus the "thank you for playing" screens after beating the game; the only adult content on offer here is [get grabbed] -> [take SP damage and get half-vored] -> [take HP damage and get fully-vored/die]. The only time you aren't going to get vored is if you die to a projectile attack or from falling off the stage, so again, if it's not your thing like it isn't mine and you're mainly in it for the game, you're going to get very well acquainted with the skip button. I guess I can say there's no shortage of variety on offer since every enemy in the game has it's own animation for this kind of stuff (minus the enemy variants like the super harpy or the lamia mage which recycle the old anims). I don't know what else to say so I won't say anything else.