If it isn't your game, then it isn't your game. That's all.
It is one of my favorite games, but that is because it does the sorts of things that I value in games. On the other hand, it would be very easy not to like Mass Effect 2 (or any game for that matter) if the sort of game it is isn't the sort of game that you like.
I loved Morrowind, and think it is one of the best games ever. But that is because I really value the complicated and nuanced way the writing team dealt with colonial and cultural politics. I also really enjoyed the ontological mystery of the Nereverine and your position as a possible candidate and all of the conflicting motivations in why you are there. All of those things I enjoyed...were missing in Oblivion. So Oblivion is not as good a game for me.
On the other hand, I know people who like Morrowind for completely other reasons. They liked the exploration. Or they liked the PC mods (which I didn't have access to because I played on the Xbox). Or they liked some other thing. I know people who prefer Oblivion because the graphics are much better, or because they prefer the fast-travel, or a more visceral combat feeling. I know people who like neither game because they don't like sandbox games, or they don't like RPGs, or they don't like Western RPGs, or they don't like sci-fi, or they don't like first person view...or any other number of things. And those are all valid.
So, there are reasons why I think Mass Effect 2 is amazing, really amazing. Apparently a lot of other people felt that way as well. But you didn't like the game--and that is also perfectly valid.
To quote Bonnie Raitt:
"I can't make you love me, if you don't/
I can't make your heart feel, something it won't..."
I can't convince you to like a game you don't like.
You don't have to like the game at all.
You don't have to justify not liking it.
And on the flip side, I don't have to justify liking it.
Now, I could give you reasons why I like the game, but I don't see what that will do.
For example, I could say that I really liked the depth of the characterization of the NPCs...but you may not have found them deep--or you may not have cared about that. Neither one of us is wrong.
I could list 20 things I liked...but none of those will change the fact that you didn't like the game. And that is okay.