What I like about ME1 is how the story was presented. It explained things before jumping into the action, but it kept the mystery of the story. My Shepard felt some agency when solving that mystery and by the end it felt good to bring down a reaper, even though Shepard knew more would be coming. It felt like playing a role. The Council didn't force Shepard, but advised him/her. When they didn't make sense you could break off the conversation.
ME2 and ME3 turned that upside down. It was like shoot first and ask questions later.
Agency was lost and TIM would send Shepard on vague missions or collect a dark and edgy crew with odd specialties which didn't appear to be useful. It didn't advance the plot and at the end you knew as much as in the beginning: Reapers were coming.
In ME3 agency didn't improve.
The goal of the Crucible was supposed to be important, but an unknown weapon with unknown power without any knowledge how to target it was supposed to be the motivation to create one and gather resources for it. Even though all species had their homeworld burning you had to gather them as allies, because reasons. Somehow Earth was more important. Even if you brought the geth and quarians together after centuries of war a brat would tell you that these geth were the bad guys and the genocidal reapers wore the white hat.
These two games felt like the story was dreamed up by several writers to fill the gaps between combat. And it appeared that no writer had knowledge of the history of the game or forgot all the previous cliffhangers. It felt like nobody read the script. Role playing had become impossible. They were nice shooters, though.
In my opinion the best part of these two was the Leviathan DLC and finally Shepard got some answers that gave the reapers some depth. It was way better than Harbinger mumbling "this will hurt you". The DLC gave the illusion that my Shepard was doing something important again.
So, back to your question.
I want the way the story was told in ME1 back. It allows me to role play. If I want to play a shooter than I rather play a real one. I understand that ME is trying to be both, but the RPG part seems to suffer. Not a fan of that.
About the combat. The bad part is that ME1 had deep mechanics, but they were poorly implemented. In ME2 gameplay was improved at the cost of depth. ME3 brought back some depth. Also, the rules of the universe should not change dramatically. Why clips were introduced and why ammo became a power is beyond me. Probably to please the shooter fans and probably because Bioware ran out of ideas to create perks, but it didn't make sense to me.
Things like biotics didn't make sense either, unless you turned down the difficulty. It feels like a minor addition to gun fights. Without guns at higher difficulty settings my Shepard felt like Niftu Cal, the Biotic God. But if your name is Jack then the cinematics of her in action make you believe otherwise. I want biotics to be just as deadly as guns and ammo shouldn't be a power. That way the differences between the classes make more sense for those who want one, the other, or both.
If MEA brings me a coherent story, agency and a bit of mystery and if the game fixes the biotics then I think it will be more of an RPG than it ever was, without making the shooter fans unhappy. That's something I like to experience.