I had this before the Steam release, and I've played more than what Steam has recorded. Planet Stronghold is a mix between RPG and Visual Novel. It's RPG mechanics are okay, and it's storyline can grab your attention quite quickly in this game if your the type to prefer story over gameplay.
The RPG mechanics are fairly basic. As you go through the game, new gear will be offered for free basically at the Armory, and that's where you upgrade your equipment. You can find a lot of better stuff by exploring the world and researching it(also basic), but the Armory stuff is enough to get you by.
It's not just "read story" and "battle enemies". There's other skills you can level such as charisma, survival, explosives, repair, science, sneak, and some others. These do not have too much use outside of combat, except for a few, but there are various events that happen, as well as side quests, that these skills can be used to change events, whether it be weakening an enemy, completing the objective/goal without fighting, getting new items, or other interesting things, theses skills are used to change how the encounter plays out. There 8 characters that you have traveling with you, and while you can only have 4 max in combat, and sometimes a character isn't with you due to story, but these characters level alongside you, and you can just have each character invest in 1, or preferably 2 of these "event" skills, and you'll rarely have trouble passing these skill checks. I still found them a great way to spice up various encounters.
Combat itself is standard RPG affair. One thing to notice is that every weapon does a type of damage, and that every enemy has different resistances to the damage types. It's very important to carry at least one of each damage type, and that every character should have at least 2 weapons with separate damage types, else they can be rendered useless outside of healing since they won't be able to do much damage against the enemy. However, they game gives you basic equipment to counter the enemies, since this is still a story driven game and doesn't want the player stuck on enemies, so there's no reason you should end up unprepared for a fight, other than your own negligence.
The story itself is okay. It won't win any awards in my opinion, but it's a good story.
Conclusion: The price point for this game is very high in my opinion(I got it in a bundle). While I think it's a good game, I wouldn't say it's worth $20. Unless your a very big fan of visual novels, I'd recommend waiting until a large sale. If I recall correctly, this game is free on android, though the Deluxe edition has extras. Try that if you can. There's also a free demo on their site.