It's the best thing out there for a room clearing CQB sim right now (at least until Door Kickers comes out). The mechanics and engines are tight. The character classes, skill development and kit building keep the gameplay interesting. Each campaign has a distinct art style, and later campaigns introduce increasingly tricky scenarios including armored enemies, outdoor terrain, and entrenched marksmen.
The main downside is that I wish there was a narrative to it. Each campaign is really just a set of five maps with the same art style. You unlock campaigns as you go, and can bounce around as you please. It's nothing like Frozen Synapse where the missions are plot driven.
As for other wishlist items, I'm sure destructable terrain would have been a pain to implement, but could have really changed gamplay. There's also no multiplayer mode (like you'd even be able to find players for such a niche game?) It's kinda strange you can't break-up or shuffle team-members short of getting somebody killed. Having to build and separately level full teams is a grindy proposition should the player want to go that route.
For those unfamiliar with room-clearing, a more theory based tutorial might be better. The devs designed the game to reward actual room-clearing tactics. In room-clearing, the objective is to stay on the attack while not getting shot in th back. If you're constantly camping behind cover, (like every-other game with a cover-dynamic encourages), you're not getting it. Get away from the fatal funnel, stay agile, and learn how to sweep geometries. If a room looks scary, toss grenade/flashbang before you breach. Unlike the old Rainbow Six or the SWAT series, there's no incentive for restraint in this game (RoE, neutrals, civilians, surrendering enemies), so let the grenades fly.
All in all, it's good little single-player indie tactics game. It's worth you time if you'd dig a fairly authentic room-clearing sim.