ME3
For me the ending was fine because I had the extended ending and Leviathan as part of the package before I got to the end the first time. There are a couple of caveats however. Since the only ending that hints at Shepard actually surviving the ordeal, the other two options were automatically non-options for me. So my complaint there is that the other two endings where never competitive for me. That did feel a bit cheap.
I was also a bit disappointed by the way the options are delivered. The intelligence took the shape of the boy that you see at the start of the ME3 and you see him in the dreams as well. I still don't get why. It was an unnecessary addition that has no value but does confuse things a bit. I would've expected at least some explanation or reference to it by the intelligence. It seems like an idea that was started and not finished properly.
Also I didn't like that I didn't get to stop being forced to shoot Anderson. At least I never managed to find a way to prevent that. The whole sequence with the Illusive Man there was actually kind of weird. Why was he there but not other Reaper forces? I would've preferred that the confrontation with him and him being controlled by the Reapers would've played out before going to Earth.
That way also after arriving on the Citadel at the end we would be confronted with the 3 possible endings right away rather than having to be pulled up by some floor panel lift to yet another area. That would've been better from my point of view.
ME:A
I hear what you say about the viability but because of the choices they made it actually makes sense. The story is a rushed one. The answer lies in what you say already...expecting to only have one planet to make viable to begin with. Because there are more planets to discover and make viable there is only so much time that people are willing to spend on it. It would've made sense to me also to have just have 1 or 2 planets to work with but they wanted to make the story big and galaxy wide and that came at the cost of quicker stops on each planet.
For me, ME:A feels like laying the foundation for a new universe rather than a continued story. My expectation is that we will get some DLC to tie up some loose ends from the current Ryder story and give some hints towards the future. Then the next installment will be the start of a new series of games with a new hero in the world that Ryder prepared for us basically. That's how it reads to me.
Having said that, I would've preferred an epic new story line spanning over multiple installments but at the same time if that were to take place I'd like to see some major changes. The Andromeda Initiative is totally uninspiring to me. I actually like the idea of using Meridian as the new home and stepping away from the Initiative. The casual white and blue are also nowhere near as inspiring as the black and red N7 gear. If Ryder were to stay on as protagonist I'd prefer them to be outcasts who have to find their own way than be lackeys for the Andromeda Initiative.
Oh yeah....
Andromeda Initiative=AI
Artificial Intelligence=AI
It's more annoying than clever in my view.