The reason *I* like ACKS is that its a sandbox for creating and running fantasy worlds. It begins like an OSR RPG, but you quickly realize there's a lot more going on underneath the hood and that the game is leading players onto bigger and better things. Characters don't just level-up, they become conquerors, and eventually kings. Want to carve out a realm of your own? Wage war against your neighbors? Become a merchant king? Research and create new monsters? New magic? Create a dynasty? Done, done, and done. Additionally, its all researched, measured, and backed-up with a lot of historical evidence, explanation, examples, and creativity.
Beyond this, its a system for creating RPGs. For example, create your own magic rules. Don't like Arcane or Divine magic? Use Eldritch magic. Don't like spell slots? Adopt spell singing/spell points; or go the ceremonial magic route. Overcasting? Check. Cantrips? Check. Corruption? Check. Oh yeah, and that's all optional. You pick and choose. And if none of that pleases you...create your own system using the rules provided. Same goes for new classes and monsters. Want to create a world where the outcome is based on the decisions you make each step of the way? Done.
Don't want any of that and just need off-the-shelf materials that are original and interesting? Guess what? Done! The Auren Empire setting is late Roman antiquity / pre-medieval, but with elements of before and after. The history is original, yet feels familiar. The pre-packaged adventures are simple to get playing, yet engaging. And there's a ton of supplemental "one-off" materials to quickly play out small encounters (remember that sand box part, above?) If you want a heroic fantasy / Tolkienesque flavor, there's a book for that. Howardian Conan-style play? There's a book for that too.
And, finally, have questions? The Patreon/Discord is awesome. The authors are always improving rules and adding new content. The community is knowledgeable and helpful.
What you might not like: Its OSR, meaning d20 vs. AC without a lot of additional mechanics. If you prefer something more bleeding edge, this game probably isn't for you. You may not prefer the race-based class system, acquisition-driven experience system, or the simplistic yet historical alignment system (law vs. chaos). If you're into mechanics like advantage/disadvantage, difficulty classes, and success levels, you won't find them in ACKS. On the plus side, this makes ACKS a game that a GM can - actually - manage in a VTT, without a ton of customization or programming needed. Its not "role play" centric, in that mechanics and rules are mainly geared around combat, magic, loot, and other material acquisition. Its up to the GM and players to build out the rest (which is, IMO, also a good thing, but you may find it lacking if your used to rules and materials that feature roleplay over adventuring.) But of course, you can always just add what you feel is lacking - the system is simple enough to make this pretty easy.
The core rules are basically FREE, so there's no reason not to give it a shot. Start simple and then "bolt on" from there.