If you loved ME2, you'll probably dislike ME3 because ME2 characters are shafted pretty bad and focus is entirely on the ME1 characters. Some ME2 characters can easily be missed actually, that's how little they matter and can be hidden away from the player.
With most of the dialogue options, you only get two choices that tend to be two extremes and it doesn't matter what you pick because after that one line Shepard will say all the same auto-dialogue stuff. Just DL the demo and try this out yourself, or hell, watch some videos on youtube. In the opening scene of the game the player gets about three chances to pick dialogue (the third choice only appears if you import). Aside those three dialogue points, Shepard says about twenty plus lines of dialogue that will be said regardless of what you pick. In fact, from the moment Shepard first appears in this game, he/she says about eight lines of dialogue before the player gets the first option to pick something. A new character is even thrown in with almost no proper introduction for the player, Shepard just knows this person. This auto-dialogue happens across the majority of Mass Effect 3 and I don't know why they bothered to put choices in at all. It's pretty clear they wanted to make this an action adventure game like Assassins Creed or Uncharted and move away from action adventure RPG.
There are a handful of retcons and several characters, ME1 and ME2, are drastically altered in really bad ways. Either as horrible pandering to a stereotyped male audience(teenage boys with holes in their pockets) or to service a change of direction when it comes to Mass Effect themes to better suit the ending.
There is so much shock value to the story, most of it is illogical when you really think about it and you can get real sick. A certain character sits and does nothing, you get one conversation, then this character dies abruptly the next time you speak to them. The game can feel unpleasant to play because of the stuff they throw at you and in fact I know a lot of people felt so worn out by it that they nearly didn't finish the first play through.
Two LI for female Shepard are completely cut out and if you import with a particular type of game, she'll only have lesbian options available. Which is great if you want to play a lesbian female Shepard, at least you have multiple options there. Not so great for the straight female Shepard and it's only made more pathetic when she wakes up in bed, alone and in sexy lingerie with a lacy butt hole(I think it's so the gas can escape).
The few things I liked in this game: Game play was the greatest of the series, loved the skill trees, <3 Paladin pistol forever, the gay romances were mature and well done(lesbian, not so much), seeing characters move around the ship and acknowledge each other's existence for once, and my female Shepard looked awesome and had lots of expressions. Though she strangely lacked them at important parts and had them at parts I thought not so important.
I just can't put myself through that awful story, destruction of favorite characters, and Shepard's voice being taken away from me again. I don't recommend it to long time fans.
