Let me get this straight: as a beat em up fan, there is no way I could argue this isn't a competent game. I need to make this very clear first, as I have a lot of fundamental criticisms for it and its design choices, but none of these mean it is incompetently made. The gameplay is clean and responsive, the sprite work is strong, the music is good, so it basically checks all the boxes for a retro throwback in this particular genre.
The glaring issue at the core of this game's design is that it is severely held back by this sentiment of "old games used to be better and so much harder". As I said, I am a fan of the genre, and old beat em ups were nothing like this.
I could bring up arcade versions of games like Final Fight, which due to the nature of those coin-operated machines, were incentivized to add cheap, anti-player traps to suck as much money out of them as possible, which is a design decision no sane person should try to emulate. Or I could bring up console beat em ups like Streets of Rage, that were designed with much fairer challenges and also offered you "continues" when your lives ran out. Final Vendetta, to be fair, doesn't have as many cheap traps as an old arcade game (the bosses can be cheap or lazy sometimes), but it does have traps and notably challenging level/enemy design at many points, plus it completely does away with any continues once you game over. This isn't an attempt to make a game as hard as the old ones, it's just an attempt to make a purposefully tough-as-nails game that looks like a classic.
I'll be honest. Making it through most of the game only to lose and be forced to restart as the default mode of play isn't particularly fun. In fact, it's quite frustrating, to the point that I was glad that the game was also fairly short. Not a good sign when someone is glad they have to play less of your game, is it? I was a bit surprised that there were only like 6 levels, and they're not exactly long. But hey, in order to unlock more of those game modes, you have to beat the game in one sitting with a specific character in a specific level of difficulty, so you better get to it.
I have other minor complaints aside from all that. For example, my only issue with the controls is that adding a block button, along with the design decisions that come with expecting the player to be able to block, wasn't my favorite. It's a mechanic that barely any games in the genre have, so it feels out of place and forces you to keep something more in mind, something that wouldn't be in your skillset no matter how seasoned you are. One other thing I dislike is how uncharismatic the game is on a story and visuals level. These characters and enemies might have been given a pass in the 90s, but they're very forgettable for a 2022 game. Frankly, the "hot ladies and beefy men" school of design doesn't cut it, it feels like you're stuck in an idealized form of the past with no nuance.
In conclusion, if you are up for a tough challenge, if that is specifically what you want, it's not like Final Vendetta is bad in the slightest. It expects and demands your best. I'm just saying this "old games used to be hard" mentality is kinda lame. There are design limitations we moved on from for a reason, and making something that's trying to bring those back, especially with those fake nostalgia, rose-tinted glasses will result in a fairly unappealing product for most people.