I definately did not like Mass Effect 2. It was too much of a departure in atmosphere, plot, and gameplay from the previous game and contained no small amount of unnecessary retcons. The first one had a very nice Star Trek/Babylon 5 vibe going for it. It had a lot of exploration, clean smooth aesthetics on vehicles, guns, armor, etc. The plot, while not exactly plothole-free was fairly straightforward and engaging. One of my favorite parts about the game was driving around on barren worlds reminiscent of mars or other real-life barren planets looking for stuff (and being absolutely terrified of thresher maws) The characters, while stock Bioware characters, never seemed over the top in any particular way, which I liked because it made them seem more plausible and relatable.
Come Mass Effect 2, pretty much everything I liked about the series got thrown out the window. The game is filled with unnecessary retcons (did the protheans really need to also be the wedge-headed collectors? heatsinks, holographic shields, etc) and unnecessary plot contrivances such as the destruction of the normandy and death of shepard were completely unnecessary and added nothing to the plot, considering Shepard comes back to be the main character anyways and the normandy is rebuilt with mostly the same crew. All of this was to shoehorn the player into working for cerberus (inexplicably retconned into beign some sort of mary sue organization with far more recources at their disposal than hinted at in ME1) and to allow for Bioware to throw in the awful darkside facial scarring mechanic from KOTOR. I found the collectors themselves to be far less interesting enemies than the Geth, which unfortunately get sidelined and retconed into being less alien creatures. Meanwhile Bioware blatently shifted the entire tone of the game to pander to the 'darker and edgier' crowd by throwing in copius amounts of swearing, sexual fanservice like Miranda, and an overabundance of 'badass' characters. Guns and equipment became less streamlined and more like conventional weapons while environemnts became significantly more industrial. The plot itself is significantly poorer than what ME1 offered, with the stakes lowered from fighting off a reaper/geth coalition to mounting an attack on a single space station. The entire plot could easily have been condensed into DLC, but is stretched thin into a full game by padding it out with the umpteen billion characters you need to recruit. Meanwhile, character customization went out the window and there is no longer any way to invest in dialogue upgrades, as renegade/paragon dialogue options are tied exclusively to the renegade/paragon meter. Combat is significantly more gimmicky with class specific ammo abilities, and inexplicable wierd abilities like the charge. Cover is much more important which makes fights much more static and less dynamic. The mako and large exploration maps are completely gone in favor of lots of firefights in enclosed spaces which makes for less variety.
All in all, I can see how some people might prefer ME2 over ME1, but the sequel was a complete 180 on just about everything I liked about the first, so I consider it far inferior to the original, in my humble opinion. ME3 just continued the trend in my opinion, sticking to or enhancing the role of aspects from the secodn that I found so distasteful and introduced a host of other problems as well which are often overlooked in favor of focusing on the issues with the ending exclusively. I hear a lot of people say that the first 95% of the game was the best game of the series, but this just makes me scratch my head, personally.