I finished ME3 again over the weekend, this being the first time I played a full campaign with any of the DLC installed, and I must admit that I found the ending to be... decent. It's still the weakest ending of the trilogy, but the Leviathan and Extended Cut DLCs addressed most of my issues. Leviathan introduces the concept of the AI controlling the Reapers earlier in the game so its introduction on the Citadel isn't a huge WTF moment. Also, I kinda like the idea that the Reapers are the product of a race arrogant enough to think themselves gods repeating a mistake they witnessed in "lesser" species, which resulted in their replacement by synthetic beings that also think themselves gods. It's not a perfect explanation, but it's better than some I've seen.
However, my main problem is still the synthesis option. I picked that option this time because it was the only one of the three endings I hadn't "experienced", and while it's the happiest ending in tone, I still can't help but view it as being anything other than thematically inconsistent gobbledygook. In future play-throughs, I'll never pick it again and will prefer to view it as being another one of the AI's crazy unworkable schemes, just like the Reaper cycle was.
One neat thing I noticed: they sped up the end credits if you have the DLC so that the credits end at the same time as the music. In ME2, the music ended long before the credits did if you had all the DLC. Also, the credits now contain a little tribute to Robin Sachs, which is nice.