I don't want a final boss with like 6 forms. That pisses me off. For example, a game series I love is KH (Kingdom Hearts)... (Game spoilers for the final boss)
In KH, you fight the villain himself. Then, you fight him again but he's angrier. Then, you fight him as a beast. Then, you go inside of the beast and fight a bunch of heartless. Then, you go back out of the beast and fight little parts of him. Then, you fight him again as the beast. THEN it's over.
It annoys the hell out of me. I want one final battle. Two at the most, if it's done right.
I also like a major cliffhanger ending. Not just a small sign that there will be a sequel. Something that makes you mad that it ended like that, but yet it was so satisfying.
In KH, you fight the villain himself. Then, you fight him again but he's angrier. Then, you fight him as a beast. Then, you go inside of the beast and fight a bunch of heartless. Then, you go back out of the beast and fight little parts of him. Then, you fight him again as the beast. THEN it's over.
It annoys the hell out of me. I want one final battle. Two at the most, if it's done right.
I also like a major cliffhanger ending. Not just a small sign that there will be a sequel. Something that makes you mad that it ended like that, but yet it was so satisfying.