I got this as part of the Game Pass subscription, and so far it has been excellent, if a little "corner-cut".
As Couch says, you can get it through MS Store (which is on every modern Windows PC), but interestingly this is cross-play with Xbox and PC (like a number of other gamepass games). Indeed, saves are (optionally, I think) sync'd between the two platforms, so I can play on my PC or console, depending on where I am. It is worth saying that gamepass may be worth it for PC gamers too, as quite a few of the games work like this.
Anyway, it opens with a small outdoor section (village huts, river, flaming forest, light puzzle, boss) that acts as a tutorial with fixed party. It looks lovely (but small) and has nice skill-based, turn-based combats. Skills are on cooldown cycles, and costs mana which is limited. Basic attacks/defend don't cost mana. Enamies are on three distance ranks, and skills are more/less effective depending on rank.
And then you create your main character... This is where the low budget begins to show. Character appearance is limited to 8 predefined pictures per class (4 male, 4 female), and they all share the same body with different faces. These tend to be same/similar face, different ethnicity (caucasian, african-american, indian/spanish and east-asian), so I found it hard to find anything I liked (no proper beards!). There is no customisation of appearance.
You pick class (warrior, ranger, wizard) and a background (perks), then apply 10 bonus attribute points. There's a nice array of skills and stats, with the 5 base attributes affecting a range of other stats. Various difficulty options can be enabled if you like that sort of thing.
Then it is on to the game proper. Additional party member(s) are added as you meet them, and they talk and fill in story/background as you go. A nice touch is that they tend to have something to say each time you rest at a bonfire.
The general feel is of Legend of Grimrock (or EOB) with turn-based combat akin to M&M. Movement is slightly laboured (smooth) which made it feel less like M&M to me and more Grimrock-y. So far, there's no overworld either which is always M&M's big thing, so whilst it *should* feel quite M&M-like, it ends up not doing so much. Still, there's enough DNA there (at least we have turn-based, party-based combat) that it keeps me going.
You'll explore the EOB/Grimrock-style levels and solve puzzles or find keys. There are levers and pit traps (again very EOB/Grimrock). The game is capable of more elaborate puzzles, but they're infrequent [ie. not BT4!].
Although it is a while since I played it, I'm reminded of StoneKeep, too. However, I can't recall how the combat played out in that. Operencia has the same good looks as StoneKeep, and similar character/NPC interaction.
Levelling gives 3 attribute points and 1 skill point to buy a new skill or passive boost.
Enemies can be ambushed if they haven't seen you. You can be ambushed if you haven't seen the enemy. Monster variety is reasonable if not massive. It feels more than Grimrock, perhaps on a par with the EOB series (but they really only had two types per level, so, erm, maybe more?), but well behind M&M. Enemies use tactics (eg. the warriors taunt you off the weaker ranged/casters).
Loot is probably slightly better than Grimrock, but probably not at M&M level.
Overall, I'd say that whilst it is a little basic and shows its lower budget at times, it is a nice game and one I'm glad exists. It is definitely one of the better GamePass day-one additions for me (alongside Mutant Year Zero), and I prefer it to the real-time-combat EOB clones that have become quite common post-Grimrock.
For me, it isn't as pure-enjoyment as the M&M games, but then few are. Since we don't look to be getting any more of those anytime soon, Operencia makes Gamepass look pretty attractive.