How good is it? Does it still have any flaws? How would you rate it?

The game is very unfinished, and that'll become clear once you play it.

A good example is that every damned chest explodes in your face unless you cast a remove traps spell first, and most chests are empty. Like they were in a rush and copy-pasted ExplodyChestsTM everywhere.

The Avatar can't swim.

Exploding mushrooms.

There's a lot of platforming, unlike previous Ultima games. At least the jumping has kinda been fixed in that you jump to your cursor. Pre-patch the Avatar would jump a fixed distance in a straight line, making platforming a horrifying experience.

Casting spells is incredibly annoying, since for fire and earth you'll have to create tokens in order to cast these spells, and they run out of charges. Thankfully wind magic is more forgiving: You have one token per spell and can cast the spells endlessly. Creating fire tokens is really bad though. I believe they somewhat made the placement of ingredients less finicky after a certain patch, but it remains awful.

The Avatar can't swim.

More exploding mushrooms.

There are only two side quests.

Combat is horrible. People can say a lot about Ultima 7's auto-combat, but Ultima 8's combat is on the other end of the horrible spectrum. It's usually a better idea to just run past enemies, since they're all slower than my grandma and you almost never need to kill anything. Not even the bosses.
There are no ranged weapons, and using offensive magic... there's no point. You'll just have to go through the chore of making more spells.

The Avatar can't swim. *gurgle*

Even more exploding mushrooms.

The world itself is boring, with the same gray caves and catacombs copy-pasted everywhere. It's also rather small.
There's only one town, and it has nothing to do, other than find important quest people.

--- Sooo....

Bitchin' aside, I grew up with this game and every so years I replay it. But I am riding on nostalgia, so I can't recommend this game to anyone. I'd give it 2.5 out of 5 stars for newbies and 4 out of 5 for nostalgia geeks.

I do love the setting, a destroyed world where the remaining people are repressed by some nasty individuals, with a bunch of arrogant titans who still think they're hot and are lording over what little of the world is left. I felt alone in that world, looking for a way out.
I also love the music, even though it's midi.

So, from the little I see of your profile I see that you've played Ultimas II, III, and VII, so you're fine playing old-school games.

As the previous commenter stated, it has some major platforming issues. I'm fine with the Avatar not being able to swim and needing to either run around walls or climb walls, but it was the first of its kind to really try the 3rd person point of view in a realistic way where you can interact with anything and everything--and it shows. Expect the UI to be frustrating to work with. Examples include dragging things behind a wall where you'll never be able to see it again or walking just one step too far which will mean you fall into the water to your death.

I am a nostalgia geek, so I may have a bit of a tainted view of it, but I do think that the game stands on its own as a dark, exploration game where the characters have interesting backstories and it's also very interesting to explore and unlock different parts of the game. If you've finished Ultima VII BG, SI, and Ultima Underworld 2, it's fun to explore yet another world that the Guardian has conquered and learn how things work in that world, and what you might be able to do to undo his machinations. Exploring the world, learning how each and every system of magic works, and trying to master each one of them to unlock other parts of the game is quite rewarding and interesting.

Of course, some of that exploration to figure out how magic works is marred a bit because the game physics don't work as well as they should. For example, there is a bit of a bug in the way Sorcerer reagents stack, where you may stack 8 Demon Bone on top of one another, but when you left-click on it to read how many you have, the UI will say "daemon bone." You only know it's a stack of 8 when you try to drag it to another location, and the UI asks you how many you want to move. Casting Sorcerer spells also requires punishing accuracy when placing reagents. Place a reagent 3 pixels too far to the left of where it's supposed to be placed, and the game does not think that the reagent has been placed at all.

Combat is a bit of a joke, but then again, it's also a bit of a joke in the other Ultima games. Once you figure out how stats work, it's easy to max them and then it's all about collecting the best items and spells to become unbeatable. I found that process pretty fun, but I guess to some players it's needlessly frustrating and is more puzzle-based than skill based.

I find the music and the voice-acting well-done to put you in an immersive, dark environment of a world where few people have any hope that things will ever get better, and are resigned to their fate in this unfair world. The monsters are well-drawn and some of the challenges are quite fun to overcome.

But yes, bugs abound in this patched version of half a game, and I sorely wish they worked another half a year on the UI to make it as polished as Crusader: No Remorse, which was created using the exact same engine, and is much easier to navigate. I also wish they released the Lost Vale expansion pack, which would have really felt the game feel more complete.