The "professional" reviews' metascore is 78, which is not high at all considering they would usually give a game like that a much higher score.
Like you said, unless you're a big fan of the series, I'd wait massive discounts before getting it.
I like this guy's review best so far:
TL;DR: Don't preorder videogames.
After just finishing a playthrough of the original 3 Mass Effect games, this game doesn't feel like a Mass Effect game, or even spiritual successor. It feels like the overdone open-world package with a Mass Effect stamp.
General nitpicks & gripes:
It looks graphically similar to Mass Effect 1, with severe performance issues and drops in areas of little consequence, like the med bay on the Ark (I'm on PC, i7-4790k, GTX 970, 16GB RAM).
Facial animations and character animations in general are just worse than the first game. In dialogue sequences, it feels like you are speaking to a robot- only their lips animate compared to the rest of the character.
The Turian and Krogan voices don't have the same bass-y undertone they had throughout the original trilogy.
"Hold to Sprint" is inaccurate- sprint works by toggling the sprint key, and remains active as long as you push movement keys. Toggle sprint changes movement to mouse-steering.
The in-game scanner has difficulty scanning an object- even when the mouse cursor is in the center of that object
Objective markers are misleading and often don't properly communicate height differences
Minute-long unskippable cutscenes take place between planets/systems in the galaxy map. Selection of planets on the galaxy map uses a limited-sensitivity cursor, making it feel clunky and limited.
Between segments of the story, you have to traverse the open-world level, which has the typical clusters of enemies and small collectibles, making the story become tedious as opposed to action-packed, like the previous trilogy.
The new dialogue system throws the Paragon/Renegade system out of the window. Dialogue options still change the conversation, but I'm not sure if it makes a difference in terms of persuasion/etc.
Cutscenes skip and perform badly, entire animations stutter.
Abilities sometimes do not work in combat, there is also no tactical screen like the previous games (the "pause" menu that allows you to command your followers mid-action).
The UI is awful and isn't explained. Navigating via unlabeled (symbols, no text) tabs at the top is confusing at first.
The cover system is lackluster- you automatically get into and out of cover, and will sometimes take cover behind objects while trying to shoot. I prefer the "button to enter cover" approach.
The story is interesting, but feels rushed- character introductions are fast, quest assignment is quicker, and there are conflicts resolved in ME3 that are brought back in ME:A (the genophage).
Weapons and armor are now on a crafting system. In order to upgrade your equipment, you have to scan objects on planets for points, use those points to unlock blueprints. using those blueprints, you must gather resources on small nodes on planets in order to craft the desired item. You can also buy the items/resources to make the items, but funding is scarce compared to ME3/ME2.
Side quests tend to be "go here, shoot enemies, find the thing, bring it back", and lack any meaningful depth.
General improvements and positive features:
Abilities are no longer on a universal timer- each one recharges independently from one another, making combat more rich.
Every character has access to Jump-jets, and the ability to hover in midair. This makes combat more fluid, allowing you to target enemies in cover with powers or abilities. With Jump-jets, you can now freely jump in the game, making level design more unique.
Every character can spec into tech/biotic/combat powers, and unlock specialization bonuses based on the skills you purchase. You can also respec these skills at any time and reconfigure your playstyle, instead of being locked into Biotics/Tech.
There is no longer a universal button. Sprinting is separate from interacting/talking.
The new dialogue system allows for more variation in your character's dialogue- Emotional, Logical, Casual, and Professional; each denoted by a symbol. There is also a huge heart symbol by dialogue that is flirtatious.
Albeit much less fun than the Mako, we have a car to drive up mountains in again.
There are forward-base drops, giving you a fast-travel point, loadout change and ammo/health restock in the field.
There is wildlife on the planets you visit, some of it hostile. Hostile enemies and wildlife can and will attack one another, letting you swoop in for the kill.