For me, it's Star Wars Battlefront. I personally was so excited to receive the game, and play it.

I played the game for about 2 days, and then EA released a DLC. My first instinct was to buy it. So, I went onto the Xbox Store, and found the DLC. It was super expensive, and that immediately wasn't very cool in my mind. Then, they announced the Death Star DLC to release in the fall of 2015. And that's when I stopped playing Star Wars Battlefront frequently.

I want to say Spore, but that game itself is already a gem to me. I can't find that many flaws in it :p

However: Star Wars Battlefront II really is a game I wanted to see rise, but being held back by the greedy EA who couldn't let us as the players play the game like we want to. It really makes me sad, because I wanted to game but looking at how it's become a "Pay-to-win" game... If I wanted to waste my money I would download a 'free' mobile game a buy everything there.
So deftly a wasted opportunity of creating a popular game, which is then ruined by greed.

MMM spore is a babe if you ask me

Why is Oblivion even an option? It's an old, fairly well regarded game that still has people that prefer it to Skyrim for the content, though it's hardly a majority opinion. Far better for this list would be the online game that they threw into the mix that has a far wider range of opinions regarding its validity in the Elder Scrolls line.

My most disappointing game was, by far, Paper Mario: Sticker Star. They screwed up the formula that made them perfect (an awesome story and great RPG mechanics, Super Paper Mario is the best one fight me) and made it absolute garbage with finite moves and basically no purpose to playing. Plus, your one and only partner is just a horrible creature and you can one-shot most of the bosses with the right item. Graphics were pretty but it was the first Mario game (other than Sunshine but that's my own fault) that I had to put down.

Stop right there criminal scum! Nobody speaks ill of Oblivion on my watch!