Massive disappointment, feels like Gears of War with some RPG elements now.
-There is no inventory or looting system, you sometimes get some weapons or armor for completing missions but enemies only drop credits, you use credits to upgrade your weapons but the upgrading is much more linear than in the first one, there are no "Ammo/Armor/Weapon/Grenade Upgrades" or stuff like that, it's mostly just "increase damage for x credits". Just before going on a mission you just get a "choose weapons" screen where you can select the weapons for your team, you can still have 1 of each type if you're a soldier and the weapon system is pretty linear so choosing weapons is pretty damn pointless.
-There's an ammo/reloading system which I think is pretty annoying, you cap at around 400 ammo for the assault rifle, 10 for the sniper so you run out pretty quickly.
-There are literally 19 weapons in the game, seriously. This is from the official ME2 info site: "CHOOSE between 19 different weapons"
-There are much, much fewer abilities and talents you can choose when you level up, in ME1 you had around 10 trees with 12 ranks each and you could specialize in weapon types, armor, first aid and much more. In ME2 however you have 6 trees with 4 ranks each, and 5/6 of the trees in ME2 is just "Improve this power (such as Push) slightly" and then you have one tree which is "improve your health/armor/charisma" etc.
If you actually enjoyed the roleplaying and immersive part of the ME1 experience skip this game, if you enjoy linear running around shooting stuff up in 3rd person with occasional 5-minute dialogue in which 3mins of that time are spent on "argh I'm dying" then get this game.
Probably would have given this a 7/10 but if you do that then fanboys just immediately go and thumbs-down your review.