Golden Sun: Dark Dawn
The first two games--Golden Sun and GS: The Lost Age--were very solid RPGs on the GBA. The first had its fair share of sidequests, optional bosses and items, a deep customization system with Djinn (if you wanted too), and very good combat system aided by the Djinn/Summon system, and a pretty decent, if basic, story. The second game increased the number of sidequests and optional bosses, greatly increased the number of items, further increased the customization with class-change items and even more Djinn, allowed for a total of eight interchangeable party members in and out of battle, along with that we got new summons that required multiple Djinn of different elements, and a bigger (if slightly more unfocused) story.
With the third game we get...a lot of the same, with very noticeable deficiencies. Many of the same classes return with the majority of Djinn and Psynergy being the same as the last games. There's only one new weapon type and a new weapon mastery system in place, and a lot of the items are copy/pasted from the previous games. The story is very unfocused and never really reaches a conclusion for any of the plot points, the dialogue drags on and on and on (not everyone needs a say, dammit!), and the difficulty is ludicrously easy. Probably the biggest things that irks me, though, is that it has multiple Points of No Return, many of which aren't hinted at until immediately before. None of the other games really had these outside of the intro areas, and even then you never missed anything of importance or use that you wouldn't be able to find or fight later.
It really makes me wonder what went wrong? They had so much to work with and expand on, and yet...ugh.