NOTE: contains spoilers
Rating: 9/10 - it was almost entirely great, very very good until it faceplanted in the very last scenes. The key problem was that it did not feel like a victory, DESPITE completing every single quest I could find.
Pros:
* Shepard's background mattered, and so many little choices were followed up on conclusively
* The characters on the Normandy interacted with each other, as well as Shepard, in sometimes hilarious ways
* I can't think of any character that didn't get a mention besides Urz, and I'm giving Bioware the benefit of the doubt and assuming he's fine
* Good plot twists
* TIM: 'You're in my chair.', Shep: '
'
* The weapon and armour upgrades were handled very well
* Character customization was great, and I really liked my Shepard
Cons:
* A hateful cover system that makes Shepard somersault in stupid directions at the worst possible moments
* The combination of EDI's new look, a 'sexier' Ashley, and a steward and reporter who invite themselves up to Shep's cabin for 'chess' and 'interviews' was over the top and gratuitous
* Kai Leng's design was utterly unintimidating, and his coat ripped off the much cooler assassin who wore it so much better than he did
** Also his (and the phantom/nemeses) rolling around the battlefield looked really silly
** I had to figure out the finer points of the controls myself because my copy lacked an instruction booklet o.O
*** THE BIG ONE: an impersonal, nonsensical ending. The result of three games worth of decisions boiled down to a single ending with only cosmetic differences, and it didn't resolve anything
Overall I really enjoyed ME3; for 99% of the plot it was the finale I had waited a long time for, but I was very disappointed that the final ending was so unrewarding emotionally, logically - and even graphically. I wish there had been more personal ending on the actual game disks than a maguffin releasing a galaxy-wide flash of light colour-coded to my Shepard's moral alignment. My personal gripes about the main game are few - I hated Kai Leng, I wanted the Mako back, and Bioware went overboard killing people off, sob - but they were bearable; the ultimate ending was unsatisfactory and didn't feel like a victory.
From an emotional point of view, I would have liked to see whether Shepard made a difference for the surviving characters she had been involved with. The generic kid representing the FUTURE evoked less-than-zero attachment for me, and I would of preferred that screen time to show what became of everyone in the end. It was also a really lonely ending for Shepard, as it turned out so badly for her, and everyone close to her.
Logically it was a pretty crappy victory. With the Mass Relays destroyed, the leftovers of the fleets would be stranded in the Sol system, with limited supplies for anyone who couldn't live off Earth-food or atmosphere; assuming Earth could even cultivate enough to support any of them. The soldiers who fought to save everyone would be unable to return to the homeworlds they had protected; in fact anyone not in their home system would have to make do. The questions raised by the main plot were left hanging; who or what was the blue generi-kid? Good or evil - was synthesis a good thing, or another form of indoctrination? I didn't like the look of Joker's glowy green eyes. What was the Catalyst really, and what the heck did it do and how did it work?
As far as graphics and storytelling are concerned, the ending was a cop out. Shepard turned grey, green, or got blown up, and the relays blew up in a flash of blue, green or red light respectively. And the Normandy landed somewhere with some foliage, also Shepard may have survived. The end. I wish the game could have given me something on what happened to the survivors, any of them.