I don't know why Sega has been hesitant to develop a reboot of the Adventure series, but if it is to do with marketing then why bother rereleasing the original games from Gamecube, excluding Dreamcast, on Xbox Live and PSN? some of Sega's choices with their games have made no sense.
But I will say I agree with people who are wanting Sega to redo the Adventure series games
as for the most hated aspect of Sonic Adventure 1, Big the Cat's gameplay can be changed so that fishing is no longer mandatory or required to beat the levels. Instead I would suggest that Big the Cat has similar platforming elements to Sonic, Tails and Knuckles, but this time he is given kinetic abilities based on which elemental shield he is using.
If Big the Cat is using the Flame shield, his power becomes pyrokinesis
if lightning shield, his power becomes electrokinesis
if bubbleshield, then he is given the power to move faster underwater, in addition to having the power to make water jets that shoot out from a pond or lake below, and push Badniks off of platforms high into the air and then landing on ground, destroying them and earning the player points.
Furthermore, his fishing rod could be used to grab extra loot at random from nearby pools of water.
But even without this elemental shields could be in different sections of a given stage act out of the water, additionally his fishing rod can be used as a weapon of sorts, being able to kill Badniks with it as if it were a baton.
I'm only suggesting how best to redesign Big so his gameplay isn't monotonous or boring for people, and in my honest opinion this would have been better if Big were designed like this from the start.
As I said this is the short version, I have other ideas for the other characters
but I don't feel like bringing all this up for now as it would be too long of an essay,
I discussed the worst character in the game because this one is the major reason why people had grievances with SA1.