Note: This story contains MASSIVE SPOILERS for both ME1 and ME2. Only read this AFTER playing the game. This story is also geared specifically towards fans of the game and gamers in general - please just skip this story if you're not into gaming (I'll delete any "gaming is stupid" or "gaming incites violence" comments without hesitation), as there's no point in commenting if you don't care about this stuff.
That is not to say it's a bad game - quite the contrary. Mass Effect 2 is most likely the best game of the year, especially in today's gaming market which consists mostly of an endless stream of unimaginative pieces of utter crap. Mass Effect 2 certainly stands out; it's a BioWare game after all, and experience has taught me that whatever they make stands out.
It's just... I'm left pondering BioWare's mission statement. "BioWare's vision is to deliver the best story-driven games in the world." Whereas ME2 makes a considerable amount of improvements over ME1, it's the story aspect of it all that suffered in the process. For a BioWare game, I found the main story to be particularly lacking. For a BioWare game, I found the characters to be particularly lacking.
ME2's combat system is a vast improvement over part one, but whether this was caused by the dumbing down, or the fact that ME2 actually has an AI to speak of, I'm not sure. The AI in the first Mass Effect, whether we're talking team mates' or enemies', was absolutely pathetic, which seriously hurt the enjoyment of it all. Enemies just ran up to you without any sense of self-preservation, and your team mates would get in the way constantly, blocking your view.
Both aspects have been improved immensely. Your team mates now take up logical, safe positions, and actually help out in combat instead of being nuisances you have to look after like a bunch of kids that need babysitting. Enemies now understand basic survival strategies like duck and cover, making them much more challenging to fight. Other additions help too here, such as the damage system where you can now shoot off legs or arms (you're right, ME1 didn't have that).
Sadly, BioWare decided that the best way to make combat more engaging was to turn it more or less into Gears Of War, and I have to say that while this certainly increases the pace of the game, this comes at a price: you have fewer powers to choose from, and the upgrade paths available to you and your team mates have been dumbed down considerably. The end result is that while combat in ME2 is fast and more fluent, it's also far less diverse and quickly started to feel samey-samey. This isn't helped by the relatively few different enemy types.
On top of that, I had several issues with the
new Gears of War duck and cover system, with Alicia Shepard (yes, I'm always a girl in games) regularly leaving cover for no apparent reason in the middle of a horde. Since I play on the higher difficulty settings, this was usually a ticket straight to the loading screen.
A really good move by BioWare was to ditch the incredibly frustrating and boring MAKO sessions of ME1. Accurately described as "a fat man on a unicycle" by Ben "Yahtzee" Croshaw, the MAKO was awful, and exploring barren wasteland after barren wasteland was tedious, and simply not fun. While the new system, where you scan planets from orbit looking for resources to afford new upgrades, can become quite tedious, it's a million times better than that dreadful MAKO.
Another major sore point in ME1 was the incomprehensible inventory system. It wasn't until about 10 hours into my second playthrough that I found out how to install weapon and armor upgrades, and managing your upgrades was just as problematic.
In part 2, BioWare improved this experience by simply not including an inventory at all. In ME2, you choose your team's loadout before starting a mission (or at key points during some missions), and that's about it. Upgrades are bought/found throughout the game, after which you must research them in the science bay. These upgrades are then applied across the board; research an upgrade to shotguns, and every shotgun will get said upgrade. There are a small number of team member-specific upgrades too.
Taking active inventory management out of Mass Effect 2 is a bold move, and one that will surely pay out in the sales department. Sadly, if you're an RPG fan, such as myself, not having an inventory to manage, not having team members to trick out and so on, is just a massive miss. ME2 will certainly appeal to a wider audience because of it, and I'm well aware BioWare employees need to eat too, but if you're an RPG nut, you'll find ME2 lacking.
In conclusion, your enjoyment of the ME's combat will greatly depend on where your loyalties lie. If you're a fan of shooters and getting right into the action, then ME2 will make you feel right at home. If you're an obsessive-compulsive nutjob like myself, and you want to micromanage your character and team mates to eek the most out of their abilities, than ME2 will let you down.