Disclosure: At the time of writing I have only played through the corruption route. I can't imagine that what I like and dislike about the game will be vastly different between routes so I'm not going to wait to review it.
This game is in dire need of a native English speaking editor.
That being said this game is a bit of a breath of fresh air. Too many html games and real porn games fall into the trap of either withholding sexual content for some retarded reason or being a glorified slideshow of gifs and webms. Seven Sins however does not scrimp on the "content" and there is more than enough meat between them to make things interesting.
The story is solidly written and interesting, syntax errors notwithstanding. If you can't quickly parse poorly translated sentences then you should probably wait for a better edited version, but if like me you have a lot of experience reading through machine-translated VNs you should be able to muscle through with few issues. Fair warning however, there is a lot, and I truly mean a lot, of text to read. I happen to like a lot of story and set-up in these games so I don't mind, but a single route is about the length of a moderate-length novella and by the time the game is finished I wouldn't be surprised if both main routes are the length of an epic poem from antiquity.
As for characters themselves it's somewhat of a mixed bag, which I'll chalk up to personal tastes. Lust, being the main character, gets the most dialogue and thankfully she is by far the most interesting. As for the rest of the cast it can be hit and miss. Some are quite interesting (for a porn game) while some I feel are redundant or otherwise unneeded. That said even the characters I don't necessarily like are usually not around long enough to bore me or are still just interesting enough to continue to hold my attention.
Now for complaints. The first is down to personal preference, but I feel like there are way too many characters. I understand this is a harem game, but I feel as though writing can start to suffer for side characters or in the worst case, the main plot and characters in favor of the side character stories. So far the dev has done a very good job of keeping everything balanced, but I do worry about future releases.
The second is obviously the syntax and spelling errors. I understand that the dev is not a native English speaker, but someone with a better understanding of English syntax could elevate this game even higher than it already is.
Third is somewhat minor but the MC will in "scenes" inexplicably become a black man, and then switch back to being white in the same scene. On occasion I've noticed multiple MC race swaps in the same scene. It's very disorienting and immersion breaking .
All that said, the game is very good. There are some very obvious improvements that should be made moving forward, but the groundwork is extremely solid and as long as the dev doesn't fumble the bag I see potential for an all time great game.
Right now it's an easy 8/10 with potential for a perfect 10/10.