An excellent game...with a few oddities that don't belong to the series.
The characters are engaging as ever, but with so many of your previous team relegated to NPCs for chunks of the game it's easy to get frustrated at their lack of screen time and their role as mission briefers in some cases. If you're a fan of Garrus, Tali and Liara, it's all good but with so many other great characters in the series...and no team Krogan in this game (Vega is your tank)...you may feel a little lost.
The missions are mostly short and snappy for much of the game with some excellent level design. Flanking and staying mobile is now an option rather than constantly defending a line like we saw in ME2. There are plenty of awesome set pieces you will encounter throughout the game that make it worth playing more than once!
On the downside, planet scanning is even more annoying, since you're objectives are pointed out to you; scanning for objects is daft since your *stealth ship* gets detected and the reaper chases are more annoying than add anything to the game (there's not even an interesting death scene if you're caught).
For me, I don't do multiplayer. Even worse, it annoys me that it has an effect on how well I do in the story.
As for the ending...it's fine, but it doesn't fit the style of the series too well. The first two games were typically triumphant (with some edges of tragedy) but it feels like the devs went all "thoughtful" and "reflective" at the end without really considering the grand story Mass Effect was trying to tell.
A tragic end to an apocalyptic war is fine, but what you're presented with does not belong here.
It tries hard to bring in the best of its predecessors and mostly succeeds...but is still not quite as good as either.