It's a very good guide overall, it even had how some of the attacks are calculated by the ingame engine. Can't say the same for its conciseness, but it does a rather good job of not intropducing spoilers. Unfortunately, it lacks on WHEN you fight the bosses, so I ended up not prepared for half of the battles, and it gives a false impression that the world is shorter than it is.

Some of the items in the game are hidden far too well for my taste, so a guide is a plus.

And yes, the Thunder Gem/Crystal bugs me too, but I've never had a problem getting them, I've got WAY too many for my taste.