What did you want to see during Priority: Earth?

I wanted to actually fight alongside all the forces I'd assembled. I also wanted something like D-Day.

See all squadmates on the ground fighting the uglies at Shepard's side

I would have enjoyed fighting through the streets of London a bit more, rather than just a few open areas.

A global wide assault (or at least continental level), with multiple tasks, armored combat (weee, mako!) and time for aerial bombardment.

Given that it takes place in London, it would have been thematically appropriate for a secret unlockable ending in which Shepard and Harbinger sit down and discuss the situation over a nice cup of tea and some cake.  If Shepard's reputation is maxed and the correct dialogue choices are taken, the Reapers would retreat into dark space with some Camellia sinensis plants and a recipe for fruit scones, and never invade the galaxy again.  However, if Shepard's reputation is not maxed or the wrong dialogue choices are taken, the peace talks break down irretrievably when Shepard and Harby are unable to agree whether the tea or the milk should be poured into the cup first.

After the suicide mission in ME2, I was really hoping for something similar in ME3.
You'd go through London fighting, meeting all your former squad mates in battle (not in one area, where there is a whole string of goodbye scenes but fighting from foxhole to foxhole, meeting all the characters as they do some epic stuff during the fight.
Also, I was hoping that Shepard would get to give out assignments for jobs like in ME2's SM. Only this time, he'd of course give them to the races that joined the fight rather then to squad mates. For example, in order to get through somewhere, they need air support from a wing of the fleet but the reapers will likely shoot down a lot of ships that will go in, who to send? The asari who might still have the Destiny Ascension (or not) or the turians with their superior tactical experience? If you have access to the Volus bombing fleet, that might be the best option though.
Later, you may need a ground force to protect your flank from reaper attack. Do you send the Krogan (are Wrex and/or Grunt still with them) or did you help the Elcor ambassador out earlier and can send in their heavy artillery units? Maybe Jack and her biotic kids are also around to offer support.
Need a distraction? Maybe Kirrahe is still around with his team or you could send Kasumi to sabotage something.
These kinds of things, what you decide and what's available to you may then determine how tough the battles are that you need to fight yourself and who of your associates and allies lives or dies.

It would have been super complicated to code and needed quite a few more cutscenes to implement properly but, this was the finale of the ME series, the culmination of 10 years of story telling. I really did have very high expectations for this one. I wasn't exactly disappointed by what we got, I do think Priority Earth is a decent final mission (right up to Marauder Shields of course) but especially given the epicness of the SM in ME2, I thought there was still a lot of untapped potential there.

There was no reason to have those goodbyes in London. When Shepard says to Anderson, "every minute wasted here, the reapers gather strength". So, how many minutes were wasted with the goodbyes? Remember the fleets are above Earth fighting. The more time being wasted, the goodbyes, the more ships are destroyed and a less chance of having the crucible docked with the Citadel. I would have had the goodbyes on the Normandy just before reaching Earth and engaging the reapers.

The tone wasn't there for the type of gung-ho finale where all team mates do awesome things and everyone cheers in victory imo. There is some of that and there should've been more involvement of the people you had led to victory or squaddies that do things, but it would've and should've always been done in the dire tone it has now where the mission leads to a stinger that sends you up to the real climax. I do like the sense of Shepard rising up alone into the Reaper nest and there's this looming anticipation over what will happen if the crucible docks as well as the heartfelt resolve of Anderson.

I really wish there had been a more ideological and intellectual conflict between TIM and Shepard in these final moments, possibly leading to a renegade Truce where you actually allow TIM to either use the Crucible himself or have him let Shepard go do it under certain conditions withiut the forced suicide and without the forced gun showdown. I also think the Crucible's function should be revealed either by TIM, the Vendetta VI or by a Citadel HUD before you rise up to the Crucible's controls and make the decision in whether to activate it or short-fuse it and hope its impact will leave minimal collateral damage as the wave hits relay after relay.

If i wanted to change the game for an ending that emphasises the team and galactic unity more i would rather change the premise to not have a Crucible, but instead smaller findings of unconventional means that can kill Reapers, like reverse-engineered collector tech that Cerberus lets you have if you use the Cipher to read some prothean codex for them or if the Rachni survived and built gigantic super-acidic hives on planet surfaces that incapacitates Reaper Destroyers.

ME3 could've been great man. They just had too much grouns to cover with less than enough time or money to do it well.

I would have like to have seen the assets we had gathered in action kind of like we saw in DAO. MEA also actually managed to do that a bit.

This. Everything you said here is exactly what I wanted for a ME3 ending mission. Basically the SM on a bigger scale. That way I could send Liara off to die on the worst assignment... er, I mean... what? =P

I would to have had a few missions before the main mission to head to the beam. A side mission involving rescuing trapped civilians. A side mission that ends with the destruction of a processing center. Another is to rescue the King and Queen. At the end, Shepard sits down with them for a cup of tea.

The final version of this, packaged in a very interesting "Orikon Collection" with a very nice streaming fix, has been released.

A month ago lol.

I am late to the party, but as I prepare for another trilogy run I was happy to see a new version number and excited to see a better Priority Earth. Donated a little cash to our friend Orikon again today, because this mod is damned good and took a lot of work.

Also has a very interesting Illusive Man "boss fight" mod WIP, check it out