After giving it some time, I thought of a few more excellent examples of (turn-based) strategy games that have a low barrier to entry, are relatively bite-sized and easy to parse. That they are as fun to look at as they are to play doesn't hurt either.
First on the list is
Wargroove, the latest game by Chucklefish. It's an indie adaptation of the classic Advance Wars formula, a series of games that were at the height of their popularity in the days of the GBA and the Nintendo DS. This game sort of plays like chess with a rock-paper-scissors element to it, in that every unit is particularly strong against some other units but extra weak against others. For instance, pikemen are a hard counter to mounted units, but get destroyed by axemen. Catapults wreak havoc on cities but are literally defenseless against air units, etc.
The game's got a lengthy and fun campaign (soon with co-op), scenarios, a map editor, robust online multiplayer and even works cross-platform. I own it on Switch and play with my brother who's on PC!
Next is
Into The Breach, the glorious roguelite strategy timebender from the creators of FTL. This game is brilliant in its simplicity. You are the commander of a squad of three mechs, trying to fend off an increasingly overpowering kaiju invasion. It's turn-based Pacific Rim, basically.
The gimmick here is that you can always predict accurately what your opponents are going to do, as they telegraph their moves and attacks. The game then becomes less about trying to predict their next move while constantly second-guessing yourself, and more about trying to make the best of a bad situation. You will only ever be a squad of 3, and enemy numbers are usually vastly superior. Moreover, mech pilots can level up and gain new abilities over the course of a run, but when they die they're gone for that run.
What's also pretty clever is that you can reset time after a failed run and start back at the beginning to try again. There's even multiple squads to unlock, and later in the game you will get to use mechs that turn the game into an extremely complex but super satisfying puzzler.
Last on my list of recommendations is
Invisible, Inc. Just the title alone makes me want to play it again, it's so incredibly clever. I don't remember the specifics too well, but basically it's a roguelite turn-based stealth action game where you play as a small group of highly skilled hackers and infiltrators, trying to thwart dangerous corporations in a futuristic cyberpunk setting.
The different agents you have at your disposal all have very different abilities and therefore offer completely different playstyles. What's most fun about this game is that as you take longer to achieve your objectives, the game's enemies start becoming more aware of you and will eventually close in on you if you take to long. You're no soldier, and enemy contact will almost certainly spell doom for you. You will constantly be battling the clock to get in and out as quick as you can, while collecting as many goodies and clearing as many objectives as you can manage. This one can be a real heart-pounder and it's all the better for it.
There's many more games I can think of, but these in particular stand out to me as perfect introductions to one of the oldest and sometimes most complex genres in gaming.
Into the Breach in particular is practically a must-play for
every gamer and it's dirt cheap to boot, so there's no real excuse not to try it!