Let's face it, if you haven't bought Mass Effect 2 by now, it's not because you're waiting on my review.
Don't look at me like that.
I want to write it, so you're going to read it.
At the time of this writing, I'm somewhere around halfway through the game. I've heard reports of the total playtime being between 20 and 50 hours, based upon how much you do. Judging by the fact that I'm already sitting at around 20 hours, I guess I know which end of that scale I fall on.
I'll give the "tl;dr" version first. Mass Effect 2 isn't perfect, but it's damn close. The few minor flaws are more than outweighed by everything the game does right. Each individual element may not hit spot-on, but the total package is one of the best games I have ever played.
Technically, the game is nearly the best available. The music is so fantastic, I almost want to buy the soundtrack. BioWare, once again, has delivered the best voice acting you'll ever find. Graphically, the game is gorgeous, but but not without its faults. Just like the first game, ME2 uses the Unreal Engine 3, though with an extra 2 years of development time. All the problems present in the first game are gone. There's no more texture pop-in and the shadows aren't as butt-ugly. Unreal Engine 3 renders "ugly" things really well. The Krogan, Turians, Batarians, Salarians, all the truly "alien" races look phenomenal, as well as the "used" areas of the game. The pretty, clean-lined sci-fi areas are beautiful and wonderfully lit, but they lack the detail and polish of the more realistic areas. The humans and "prettier" races just seem a bit off. Whether a limitation of the engine or BioWare's programming, the faces just don't seem right. The combat animations are perfect, but for some reason, Shepard's out-of-combat movement looks like he belongs in the Special Olympics.
Again, it's not perfect, but it's so good that it doesn't detract from the overall game.
BioWare is the best in the business at writing stories. ME2's scope is so grand, it's almost too much to wrap my mind around. BioWare has not created a story, not a world. They've created an entire universe. The planets, the races, everything meshes together. I'm sure if I spent a weekend reading through the Codex, I would be further amazed at the amount of detail. With all the groundwork laid in the first game, ME2 better develops the individual characters. Every member of your crew has feelings and a reason for being there. They have good and bad qualities, as well as real issues. Each crew member has their own side mission that really expands the character. The only issue I have here is that the side missions are too easy to acquire. I'd rather see them as part of the dialog progression, much like in Dragon Age: Origins.
Shepard is pure win this time around. He's focused on the mission. So much so that, occasionally, the "neutral" responses will result in Renegade points. The dialog interrupt system is fun. At certain points in conversations, you can pull a trigger to interrupt the scene with either a Paragon or Renegade response. It gives the player more control over the story interaction and adds a bit of fun to the dialog segments. The characters are more animated during conversations, as well. They will get up, walk around and otherwise physically react to the conversation. The only odd part is everyone having to "reset" back to their original positions for the next dialog thread.
Gameplay has been discussed to death many times over. Some people call it "dumbing down" while others "streamlining." Some lament the loss of some RPG elements in favor of more of a pure shooter. Honestly, I'm entirely in favor of the changes. The shooting in the first game was a bit clunky and the action was slowed down with the constant menu diving. In ME2, it's pure action, and smooth as can be.
The equipment customization is done almost exclusively between missions. I have two of the special armors, the Blood Dragon and Collector sets, but I'm not even using them. Customizing Shepard's standard N7 armor is too much fun. Finding new pieces for weapon damage or shield strength, deciding which to use and making my Shepard unique is the highlight of the changes for me, thus far. Weapon customization is a bit of a mixed bag. You don't buy new weapons, but rather find new versions. Unfortunately, they're few and far between. Almost twenty hours in, I'm still using the starter Sniper Rifle and SMG. Researching weapon upgrades is a nice touch, but too linear for my taste. There's a standard progression you follow, with no choices to be made. The thought of choosing your weapon loadout, deciding between accuracy, damage or other effects would have been a great use of the system. As it is now, you definitely feel more powerful, but in a game that's all about choice, having such a large part of the game completely on-rails is a bit disappointing.
The best thing to come out of this system, though is it upgrades your entire crew all at once. Without having to maintain each individual character's equipment, you're free to choose whoever you want to bring with you for each mission. Fighting Blue Suns? Bring "Archangel" and Miranda. Blood Pack? Grunt and Mordin are a great team. ME2's combat is so reliant on weapon, ammo and skill choices, that this feature is vital to strategic gameplay. And you better have a strategy. Enemies are no joke. I've noticed my Infiltrator has far less survivability that in the first game. Proper skill usage and cover management are vital to success. At first, I was unsure about the new "heat sink" system, but now I see it helps balance the game. My Infiltrator used the Sniper Rifle almost exclusively in Mass Effect. Only getting ten shots without having to find some more clips makes me save that powerful weapon for when I really need it. It's a big shift and takes some time to get used to, but it leads to a better game, in my opinion.
Then there's the planet scanning. Nobody likes planet scanning. You need to scan the surface of every planet you come across, searching for resources if you want to research upgrades. This takes F-O-R-E-V-E-R. While more realistic and less annoying than the old Mako segments, it's not necessarily better. That said, I've found a few ways to make it more bearable. First, make sure to research the Scanner Upgrade ASAP. Then, instead of holding down the scan button, click it while moving the reticle. You'll get a quick scan of the surface, and still catch the major deposits, which is all you really should be looking for. It's a waste of time and probes to search for every tiny deposit. With this method, I can take a planet from "Rich" to "Depleted" in 2-3 minutes. I could do without the system altogether, but I've at least found a way to make it reasonable.
At the end of the day, Mass Effect 2 is just a brilliant game. The whole truly is more than the sum of its parts. It's more of a shooter than an RPG at this point, but that's irrelevant. It's fun, it's engaging and it tells a great story.