Gameplay:
After a fitting introductory sequence, my hero "GAKU" set out to save the three kingdoms. The gameplay itself is easy to master. In addition to 4-direction movement via arrow keys, you only have two buttons to worry about: the select/action button (spacebar, or "A" on my joypad) and the cancel/menu button (x key or "B"). "A" lets you talk to NPCs, search your surroundings, and select options in battle. "B" pulls up the menu or cancels selections. Since most battles involve pressing "A" on the default option (attack) and scrolling through text, you'll find yourself mashing the A button repeatedly in most battles, especially while grinding for levels. That brings me to the main problem I have with this game...

If you want to stand any chance, you have to grind excessively. In my opinion, grinding for the sake of grinding is fine if you're playing an open ended game (like an MORPG), but in a game with a beginning/middle/end, grinding does nothing but waste time that could be spent playing through the game. For example, in one town, buying the entire Iron equipment set costs 1250 gold; at an average rate of 7gp/battle, that's ~180 battles with local monsters. Of course there's no requirement that you stay and get the entire set before moving on, but given the general difficulty of monsters, you won't want to risk moving further until you do.

Why won't you risk going further? - because Regressia is surprisingly unforgiving. Having grown accustomed to BYOND RPGs, I expected to be revived at the local inn after being killed in my 3rd random encounter (yes, third, in the starting area). But no, once you die, you're dead for good. Continue restores you at your last save point, but you lose all progress since your last save. That's nothing unusual for an RPG on the NES, but when was the last time you saw a BYOND game with "hard mode" enabled? Expect to make a LOT of trips to the inn. Also, if your first purchase is anything other than the Copper Sword, I suggest restarting the game. If you aren't used to the old-school NES style of RPGs, this might take some getting used to.
A lesser issue is that some of the monsters could use a bit of balancing. For example, monsters in one area do 1 damage to me and yield 40exp; monsters in another area will drain all of my HP and then some but only yield 100 exp. The solution is obviously to grind on the weaker monsters, but given that most of your levels don't give you any meaningful stat increases (see above), expect to spend the vast majority of your time mashing the "A" button while pacing back and forth.
I don't mean to sound overly negative, but I wanted to get all of my gripes out of the way first. Despite these issues, Regressia is an excellent game, and it's obvious that a lot of time and effort went into making it. The story is certainly above par for a BYOND game, and the game itself draws you in like few others I've seen on BYOND. The fact that the content is 100% original makes this even more astounding. And as a compulsive explorer in RPGs who always goes back to take the "wrong" path, the game has plenty of secret areas and hidden goodies to keep me occupied. I found myself revisiting areas multiple times to solve puzzles and collect hidden treasures. Gameplay gets 9/10 because it's straightforward without compromising quality, content, or enjoyment.

Presentation:
As I said above, Regressia has the feel of a NES RPG, and as far as BYOND games seeking to emulate NES RPGs, I would certainly place Regressia at the top of the list. Even when compared to actual NES games, Regressia easily holds its own. Had this come out in 1987 on the NES, by today there would probably be a whole series of Regressia games as well as an MMORPG in the works.
The original graphics and music fit perfectly. The HUD interface is seamless. One thing that always drove me nuts in Dragon Warrior games was having to bring up the menu to talk to NPCs or perform searches, and I'm very glad to see that Regressia went with the more sensible "action button" approach. The attention to detail is obvious when reading books and NPC text, and I can safely say that few BYOND games are anywhere near as polished.
Originality:
Virtually all of the content is original. Although the game is made in the style of the generic NES RPG, I don't see this as a reason to deduct originality points. (No modern game is absolutely original since it will contain at least some elements of older games.) But considering Regressia's peers (mostly rips and fan games), I don't think a 10/10 for originality really does this game justice.
Overall:
This is an amazing game that I would recommend to anyone. It does have some issues (see above), and the only reason I'm not giving it a perfect 10 as an overall score is because of the grinding issue. If you haven't played it yet, give it a try, and if you have played it, I highly recommend paying the $10 subscription fee to access the last ~4/5ths of the game. In summary, congratulations to Iain for creating what I consider the most enjoyable and most polished standalone game on BYOND today.

What I mean is, the free demo is a lot less than 1/3rd of the game, closer to 1/15th or less.