The first Mass Effect was a bittersweet affair: coupled with the fantastic story, writing, action, graphics and world were terrible texture popup problems, tedious and repetitive side missions, tons of micro-management and some interface issues. That didn't stop it from being one of the best games ever created back when it came out, but it still kind of hurt my overall enjoyment of it.
Now we have this game, which by not only fixing these issues but also improving everything else has easily earned itself a slot in my top 5 games of all time list. Popup is completely gone and lighting is drastically improved, side missions are all unique and fun, micro-management is reduced to the essentials and the UI is streamlined very effectively. Combat is much improved and more visceral thanks in no small part to the superior control scheme, and also makes a more frequent appearance. Conversations now have new options to interrupt NPCs and are generally better written and more interesting to listen to. Voice acting is phenomenal. The story is captivating, perfectly structured and full of twists. Characters are each more interesting and fleshed out than the next. Need I go on?
There is one small flaw to the game: the resource mining mini-game. The problem lies in it being more like a slow and tedious mini-job than a mini-game. It's never as bad as the Mako missions from the first game, but it's something to be improved upon in ME3: make it fun, damn it!
When you consider that I spent a total of 38 hours (a personal record) playing this without ever getting bored, and that I've even started a second play-through within the same week, I guess there's no real trouble in saying that this is one of the top 5 games of all time. It is probably the single most incredible achievement in video game narratives that I've seen, and is without a doubt a must-play.
In a sentence:
An incredibly vast array of fantastically written and captivating story possibilities supported by a sturdy and fun combat system and jaw-dropping graphics. Without a doubt the most narratively fascinating and complete game ever created.