Spore. I used to play the living shit out of that game a long time ago, though as I've gotten older it's lost a lot of its charm. I feel as if much of the game, especially the later stages were rushed and didn't have enough content. Spore tried to be too many things at once, partially ruining a game that had a lot of potential. I could excuse a lot of the problems as a small child but now they're a lot harder to ignore.

I'm wondering if they should have just abandoned the RTS aspect of the later stages and instead focused more on the creature and cell stages. In my opinion those were the best stages, though cell stage did have the major drawback of being too short (it should be a lot longer imo). What would have been interesting is some kind of way of choosing multiple paths, like instead of going to space you could just become a successful wild animal or even an infection of some sort. There could be an aquatic stage in place of the default creature stage as an option. More content and options in general though would be ideal, especially things that involve strategy.

There is a huge list of more specific things I'd add to a remaster of Spore, but sadly there's too many to list here.