I personally cherished this game in almost every way. I played it after JC2 and found it oddly charming and fun. It's got a nice setting and scenery, as well as decent graphics for a 2006 game. Audio was buggy like there was no tomorrow, but I found it humourous. The gameplay was... unique in its own little way, but I enjoyed it for the most part. The particular mechanics definitely make it seem like the prequel to the awesome Just Cause 2.
The characters were cheesy as all hell, but I think that adds to the game's overall style. The story could've been better, but after all, that's not what the Just Cause series is about, now is it? I think that the story served its purpose in letting you know why you're on an island blowin' ♥♥♥♥ up.
There's plenty of things to do, making it a completionist's dream. However, if you don't like repetitive missions/objectives, then you might get less time out of it like I did.
Overall, it's a classic title for anyone that liked Just Cause 2 and wants to discover its roots, or to anyone who wants to get into the series.
I fully recommend it for the price. Definitely worth it!