As a veteran Into the Breach player, I jumped into this thinking I knew everything and inevitably got slapped by the mechanical differences.
Writing this review as of 100% completion of the achievements list (and yes, I'm aware it's only been out two and a half days), I robustly recommend this under its own merits.
Mechanically, it shares a lot of its base structure with Into the Breach. Its core loop is roughly the same, though with a set map path. It has nearly every damage type, tile action, and mission event as its compatriot, but adds a lot of new ones (for example, things that might be called escort missions broadly have artefacts like cannons which have their own free move).
These similarities are not a bad thing, especially with the game's hero system/party composition allowing for more interesting setups with far greater freedom of choice at the start (a trade off, of course, for less flexibility later on). The addition of the four man (well, three and an animal companion) squad also allows for some really interesting teamwork.
Currently the game has four unique bosses, each of which is solidly designed, but always in the same place and always accessed by the same route. This isn't necessarily a bad thing, as each attempt will always be a little different, but if future additions are in the works then more variety would add to the game's appeal. Steam doesn't let reviews have enough words to write a full breakdown of the changes and additions to the mechanics, but its not hard to pick up in play.
The game plays clean and I've yet to encounter any crashes or major bugs through multiple game clears. The achievements are fair and can be acquired reasonably easily (though some take a little patience... or the lack of it in one case).
The one issue I would pick with this game is its lack of a manual (at least, as of its release state). While there is a tutorial which admirably covers the basics, certain mechanics aren't explored in depth and the damage calculation formula isn't always clear (for example, if you push a shielded enemy and deal damage in a single move, it seems to calculate the push damage separately from the rest of the attack, allowing you to wound or kill the target unlike Into the Breach's all in one calculation). This I suspect will likely be overcome once fan guides and future support are in place.
As such, I wholeheartedly recommend this game, especially to grid-based strategy fans!