I recommend you play Mars War Logs before Bound by Flame, but definitely still play Flame, not because Mars is a good game or even Flame is a good game, but because GreedFall is a good game and Steelrising is a good game. You cannot fully appreciate Spiders' journey over the past 10 years without going back to the beginning.
For those experienced with Mars, here are my reasons why Flame deserves 4 stars while Mars only 3:
1. The background story is more interesting and the game's plot is more cohesive. No transitioning from one act to another and suddently the world is upside down, and your MC is introduced to political struggles you didn't even know he had.
2. Your have more companions and they are more fleshed out from the game's beginning, instead of crammed in at the end of act 2 with no chance for you to care before the game ends. In fact, your companions can die before the end of the game.
3. Perhaps the most important, you can cheese your way through all the combat of the game. I use the term "cheese" fondly. By that I mean as a RPG player you don't have to "git gud" to progress in the game. You still can; there are ample opportunities. But by carefully managing your skills, your companion, and your crafting items, you can easily eliminate every enemy and boss in the game with the right strategy and, in some cases, a bit of patience. I just did on Buffalo difficulty. In fact, you can bypass every enemy in the game other than bosses, though your XP and progression will suffer. Gone are the incessant small arena-type locations in Mars, gated by doors and ledges that you cannot interact with in combat, so once combat starts your only choices are win or die.
4. Oh, and the music is fantasic. Haunting vocals. Try to find samples online.
Without a doubt, there are better action RPG out there for the same cost in money and time. However, I played GreedFall before, and after Mars and Flame, Spiders is becoming one of my favorite action RPG devs, for their growth.