But, to start with the basics, the mechanics. I really wasn't pleased with a lot of the combat changes that they made between 1 & 2. I am an RPG fan, I like a lot of RPG elements, and realizing that a lot of them had been removed didn't make me very happy. The first game gave me a lot of room to customize my characters, and #2 is sadly lacking in that department. There are many fewer abilities, and many fewer points to allocate between them, and even at the end of the game none of the characters can possibly achieve mastery in all of their skills. Once I hit the level cap, I ended up using a research terminal to reallocate the points of every single member of the party, which thoroughly suffocated any sense of "natural" progression.
I also found combat to be much more frustrating than in the first game. I'm not complaining that the enemies did more damage, and that casually walking along outside of cover was a great way to die. I understand that, it makes sense. But it really sucked because I had continued using my class from the first game, vanguard, where my focus was on assault tactics. Part of this problem was that it took me a long time to understand how to effectively use the Vanguard-specific power, Charge. I had assumed that it had a much shorter range than it did (don't ask me why, since the range was clearly listed), and so for a lot of the game I couldn't effectively close with enemies and ended up fighting at longer ranges, where I was at a disadvantage. Of course, Charge itself is sometimes more trouble than it's worth. It's area of effect is strictly limited, and I died frequently because I found that after charging I had enemies targeting me and had to wait ~6 seconds to get a barrier up. Never mind that Charge only rarely seems to inflict any damage, and trying to quickly wheel and shoot anybody else around while still worrying about the guy that was knocked over was aggravating. The game claims it's a "high-risk, high-reward" maneuver, but what is the reward? Killing the enemies slightly more quickly? Maybe in some missions that might matter, but in general the game made me feel like a chump for not sitting back with a long range weapon and pretending I was in a shooting gallery. Was a hell of a lot of fun to use on groups of Husks, though.
Also, while I'm bitching about class balance, I got really, really sick of shooting someone point blank with a shotgun and them not dying. And this was with a DLC shotgun, and not up against armor or shields. A good shotgun in #1 and I would ruin anyone within about 5 meters, much less right next to me.
All of that said, though, sometimes it worked. Like with the first game, I generally let my squaddies handle themselves, and in general they were pretty helpful. Also, the addition of the submachine gun, especially once I had the long-range gun from Kazumi's DLC, made the range combat much more tolerable and was a big help when I couldn't run in. Getting the sniper rifle also helped.
Also, having heavy weapons made fights against many of the big gribblies more bearable as well. It also made sense: why wouldn't the squad take heavy arms into the unknown?
Now, onto the plot.
I actually really liked the sense of narrative time, where you generally have the opportunity to fly around and do what you like until the Illusive Man interrupts with an important mission that you have to do right away. But I got tripped up after getting the Reaper IFF. I hadn't anticipated the crew being kidnapped, and so I wasn't entirely ready for the final showdown when it happened. I then got caught up on a few bits of video game logic. First, I don't know that I had ever encountered a game before where doing too many missions in the "final act" is actively punished. I assumed that I wouldn't face consequences for delaying the final mission in order to finish, as we call it at the Icebox, "mowing the lawn". Second, I assumed that once the game was over, it was over. There are some games where after the final showdown you have the opportunity to go and do more missions, but I didn't assume this would be one of them: to the best of my memory the first game was not. Third, the introduction of Legion on the Derelict Reaper threw me off. I assumed that a permanent party member would not be introduced right before the end of the game, and that I would be given time to "field-test" Legion before doing his loyalty mission or making the final assault.
And so, after doing several hours of additional playtime past the kidnapping of the crew, I cheated. I went to the Mass Effect Wiki and checked to see what would happen with the crew. When I discovered, to my horror, that the crew were now long dead, after some agonizing I reverted to an earlier save. I was initially unhappy, until I remembered that I actively enjoyed playing the game most of the time. As Genghis summarized, "oh no I have to eat more of this delicious cake". But, like cheaters do, I now feel a little sad about how it turned out. I saved everyone, no one died on the final mission, and all because I refused to be caught flat-footed. It feels too artificially perfect. If I could do it over again, I'd have gone and done Legion's loyalty mission after the crew was kidnapped, and then gone to take care of the Collectors. That was the ending I should have had (I no longer have an appropriate save to do this from), though I'll take the ending I go rather than the one I should have had.
Other stuff. The Paragon and Renegade QTE options are brilliant. I missed one or two because I wasn't paying attention, and I didn't take all of them, but they were well implemented and characterful. I also liked that even when it was a Paragon option, sometimes Shepard was still a badass.
One of the highlights of the game for me happened on Ilium. (Huh, spell-check recognizes that word? Why?) Specifically, the quest entitled "Blue Rose of Ilium", where the PC can give an Asari merchant advice about her love life. It really did a good job of making me realize that the galaxy Bioware has created is still mostly filled with normal individuals living and working ordinary lives: that not everyone gets to, or wants to, be part of the big adventure. For most people, the ancient concerns of life, love, wealth, and status still dominate, and they're doing what they can to make good on them in one way or another. Also, specifically referring to the Asari, it made me realize that a 1000 year life span is a very long time to be poor, or lower class. Even if there is some mobility across the centuries as opportunities present themselves, there are still some people that are probably left out.
An interesting change of tone from #1 to #2 is due to two big shifts. One is in PC perspective, since they no longer work for the official human military but instead work for a shadowy paramilitary/terrorist organization, Cerberus. I found it frustrating that for most of the game you have limited ability to influence the organization, despite the game implying that you command one of their larger cells. Also, every time a character asked me why I was working for Cerberus, I never was given a conversation option that remotely justified why a Paragon-tastic Commander Shepard might be doing so. At best I could deny it, or say I was working with, not for. It didn't help that Cerberus seems to have conducted a great number of experiments that they either completely botched (as in the DLC Overlord), or that must have had unsound project goals in the first place, such as the experiments with Rachni, Thorian Creepers, and Thresher Maws in the first game that are referenced again in the second. Nevertheless, the Illusive Man, at least, seems willing to throw good lives after bad, and apparently there are no shortage of human scientists and engineers that are smart enough to make breakthroughs, but not smart enough to notice the mortality rate.
Also, I mentioned in my review of the first game that corporations generally acted as villains. Here, while there is some discussion of Corporate malfeasance (and it's worth remembering that Cerberus is largely funded by corporate profits), the status as secondary villains is reserved for mercenary companies. Three are identified, each with a distinctive fighting style, and each are shown doing generally deplorable things. Sometimes, there is clear economic or personal incentive to do so, but not always. Mostly, I think the tonal shift is a smart move on Bioware's part, making the game more appealing to a wider part of the sociopolitical spectrum.
I am going to start wrapping this post up now, because I've said the most important things I can think of, and I'm sure I could go on all day. This game is so big, and the elaborations of the universe are so interesting, that people could, ad probably have, written formal papers on it.
So, in summary, I really, really liked the game. I don't think it's one of my favorites ever, as there are too many niggling concerns. But the subjects covered will get you thinking, and the action should be good enough to appeal to most players.