I've been on a drawn-out Bioware kick. Since 2014, I replayed a Bioware RPG once a year: Knights of the Old Republic, Knights of the Old Republic II, Mass Effect, and most recently -- this spring -- Mass Effect 2. All of these are fine games, but Mass Effect 2 is something special.
Here are the high points.
Much better ambience than the previous game. Settings are richly detailed, colorful, atmospheric, lively, varied. No more identical cubic cargo holds full of cubic cargo, and no more of the sterile silver corridors of the Citadel. Now it seems as if generations of people have lived (and died; died a lot) in the environments. There are some memorable locations, too, like the rainy prison featured in Jack's sidequest or the precariously-perched crashed spaceship you find while scanning for minerals.
The Normandy is much better to walk around in. Within it, there's much more to see and do. Chatting with crewmates is actually fun and has some variety -- more than a few lines of dialog. This recalls the days of Knights of the Old Republic 1/2.
The "overworld" map used to bring your ship between worlds is much better. If nothing else, it has progress tracking (e.g., it shows that 33% of a star system is explored).
You no longer need to do bullshit driving missions before starting your bullshit shooting missions. Now it's all bullshit shooting missions.
Even if combat is more tightly integrated into game, it seems like there's less of it, and less tedious running between firefights.
The story is nonsensical, but it's easy to follow and reasonably engaging. And it's still the best one in the series. But where the game shines are the side-stories. Sidequests are genuinely interesting. Most of these also have a real bearing on your relationships with your crewmates.
Sooner or later I'll find the time for ME3.