Aye, I remember playing twice through it - once with Edelgard, once with Claude - and after that read what the other possible stories (Dimitri, church) were. There's a lot of overlap, but you get new bits out of everything. I guess Claude gives the most purely in terms of information on what's happening in general. Definitely a great game.
on topic: Guards - 6/10
A bit difficult to rate for me. On the one hand, I loved it. It's a roguelite with turn-based combat. You choose 4 out of 8 heroes and go on missions, try to get as far as possible, get rewards, upgrade them, and start a new mission, etc. It really had the "just one more mission / run" factor, as I enjoyed the (admittedly very simple) gameplay.
On the other hand, there are quite a few negatives to it. First, there's not much variety to it. There's only one map, you take the same route every time, the same 10 battles - only spawn place and units vary a bit, though the pool of possible units for each map is the same. That gets repetitive real quick. It's also fairly annoying, that you get a lot of mythril (currency for more or less everything) when clearing a map the first time, but repeated runs only give very little. As upgrading your heroes costs a lot, usually you try around early and stick to those you like. To also level others can be really grindy. It really limits experimenting, and makes the game get boring even more quick, as you're fairly stuck with your leveled heroes.
But, it's just 5 bucks at full price, for that it's quite good and some limitations are expected.