My opinion may be biased as I was one of the artists involved in that book, but I do own a copy and it's very, very good.
It includes very detailed Naval Rules, lots of crunchy bits as ships (including some aerial ships), PrClasses, new monsters, equipment, spell, magic items and stuff like that.
It also includes lots of NPCs and Nautical Organizations and expands upon the Twin Crowns setting (but the book is 100% usable outside the setting anyway).
I was only involved as an artist and I was very happy with the result of the book. It's been used twice in my game (but we only had two sessions since I got my copy)
Thanks for the post, Antra! I like your artwork (though I wish you had used some of the cool pencil shaded pieces in Broadsides!).
I'm very eager to get Broadsides, as there's been a lot of hype over it. My players are still wondering how I'm going to work nautical rules into a mostly landlocked game...heh heh, wait until they find out.