I recently had the opportunity to playtest Planet FIST, and while the session hasn't been finished (yet), I have a lot of good things to say about the game. First off, it strongly embodies the player freedom afforded to players in the base FIST game, and with a highly similar free-form combat system, it's a simple matter to pull off any number of daring trickshots or complicated maneuvers. Unlike FIST, though, the playing field itself is much more grounded, which makes it much easier to understand what's going on at any given moment- I would even say it's reminiscent of games like LANCER, even moreso given the sci-fi aspects.
As for the aspects outside of combat, character creation was incredibly fun and I loved working with my teammates to create our squad members. It was so engaging, in fact, that I practically forgot about the mission part! All the traits add huge amounts of depth to each character, especially bonds that connect all the members of a squad together. I'd be hard pressed to find any real grievances I had with any aspect of the game.