BoboTheMighty
SasqWatch
You got that backward. Each game has improved combat over the precedent one.
Mass Effect 1 as probably the worst implementation of cover shooting ever made. Not only is it bugged like hell, it's awfully clunky to use too. It has like 2 enemy types - humanoids that attack at a distance and stuff that rush you (rachni, husk, creepers) - and shooting your pistol is the fastest way to kill anything in the game regardless of class. I replayed it twice last Fall.
ME2 is an improvement in term of usability, but still a bit clunky (Vanguard charge and squad-mate abilities targeting is finicky). It adds more variety in term of enemy types forcing you to use your class abilities to strip defenses or switch ammo/weapons and offer more individuality to classes. ME3 is a polished version of ME2 systems with more class individuality and a few more enemy types (like centurion and banshee).
The squad AI is dumb like a brick in all the games.
MEA, going by the video, is build on ME3 with a new cover system, more melee options (it was class based in ME3) and a jetpack for more mobility and a vertical tactical option. I'm not sure what you call a downgrade among that.
Wouldn't say, in every respect, but they got better overall. With ME I Biotics physics were better, (or at least more believable), than shoot a blue magic ball out of your hand. Liked also stamina dependant sprint, more run and gun approach, sniper rifle requiring more skill and few enemy types, like those jumping Geth.
ME II was more Gears of War inspired and improved shooting/cover mechanics, improved classes/weapons, was overall faster, more polished, with better controls and targeting systems.
But was too much pin to cover and wait for enemy to show it's head in reg intervals. And without good flanking AI and fast shield/health reg...
Also, didn't like added magic powers...fire/freeze/etc ammo... too gimmicky. Vanguard was a rush though, 6 sec cooldown was timed just right to let you escape death by an inch...if you're good, or get killed otherwise.
ME III expanded on it and made it more open without being fully restricted to cover. But Imo, cooldowns were way, way too low...it removed the When? to use powers to simply spam...ruining classes like Vanguard( even if pulling Nova's were a blast).
This seems overall the best, jetpack a great addition...pulling up in the air and shooting seems crazy fun and open world with obstructions allows lot more freedom in approach.
With some improvements in gunplay, AI and animations, could be one of the best TPS out there.