As a general and positive statement, I'd say Forbidden Lands is one of the best fantasy games I've played, and I would pick it to play before playing Pathfinder or any mode of DnD.
It is not perfect, and it may not be for everyone, however.
We have played FL for a about a year, and what I find that I value most is how "efficiently" it plays. By this I mean that I feel like it is one of the rare systems that we seem to get a lot done with our few hours of game time rather than spending a lot of time flipping rule books. The mechanics are clear and task resolution via dice is fast. Combat is equally fast (usually) and endemically dangerous enough that players will quickly learn that perhaps combat is not always the best solution to a problem.
One of the very subtle things we value about FL is how it very purposely injects chaos into your game from unexpected quarters. This is hard to explain, but the advice in the rulebook to "prepare less, and let the rolls guide you" (paraphrased) is kind of true. I think it's a great system to run a good sandbox game with (and, clearly, this is a design goal of the game and it provides you with the nerd knobs to do it fairly easily).
The provided world is detailed just enough to get you started, but intentionally mostly up to you. The wealth of published material, both official and by the community, is strong for a comparatively "small game". If you only picked up the base box and Raven's Purge (which you should), you have a complete game and massive campaign to run from the get-go.
This is not to say the game is universally adored even at my own table. One player is a little hide-bound by their experience (mostly with D&D games) and personality that causes some friction/cognitive dissonance with the rules. In particular, this person has trouble with the Push to gain Willpower mechanic (a mechanic I, as the GM, actually adore because it causes players to willingly inject that oh-so-tasty chaos into the game by their own choices).
I encourage you to play it long enough to direct your players through the first two (of three) sites in the GM Guide. Start them somewhere and nudge them towards The Hollows (causing them to explore the map a little). From there, move them towards Weatherstone with the idea of having them realize they can make it their stronghold. At this point, you've set them up to play in the Raven's Purge sandbox and you've got months of play ahead of you.