First general lore discussion topic and its focused on ME3. Interesting.
Most people are wrong when they say ME3 was good for 99% then the ending sucked. The writing started sucking back in ME2 but lets not go that far.
"Sucking" is purely subjective. Therefore no one can really be wrong. They just have different opinions than you.
The whole point of the first game was to stop Sovereign from reaching the Citadel and opening it as a relay to dark space where all the other reapers where here they explain that they could shut down all the relays and cripple the organics war effort. Well why didn't star child just do it? Another plot hole the size of Lisa Ann's birth canal.
Indeed why did the star child not do that. Though this is a problem of the ending specifically.
But back to ME3. If the reapers just attack the Citadel first they could have shut down all the relays cutting off any way for anyone to move around the galaxy and thus winning the war. IT MAKES NO SENSE. I would like to sit down with Mr. Walters and ask these questions because I have lots.
The real answer is very simple and not something you'd like. The reason the reapers don't attack the citadel immediately is because its a video game and if the game was really over the moment the intro began... well, thats no fun. Certain liberties are to be expected. To have a more in-lore explanation one of the best ones I can come up with is the fact that the reapers are patient and gradually making their way to the Citadel. We see them slowly closing in towards it during the course of the game.
Another thing to consider is that the species currently controlling the Citadel do not realize its significance. Oh sure, Shepard knows, but lets face it... the council hasn't been paying attention to any of it. If the Council manages to predict the reapers rushing in they might be able to close the arms before the reapers can 'dock'. Sovereign barely made it. If they don't get in before the arms close then the reapers are in a bit of a pickle.
Attacking their homeworlds causes them to divert focus to protecting their planets, underestimating the worth of the citadel. Everyone's more focus to protecting their own homeworlds than they protecting some space station. So with all the governments striving to protect their worlds their security on the citadel lessens and the reapers are given a chance to swoop in and take it before they have a chance to act since they're more focused on their worlds.
Also consider the reapers tried taking the Citadel without risking themselves by working through Cerberus.
See now it made a little bit more sense if they stuck to Drew Karpyshyn original plot of the reapers needing to find a way to stop the spread of dark energy by going to earth and making a human reaper because they were running out of time, and they believe humans were the way to stop it.
Still sucks the big one but it made sense why they would needed to go to earth before doing anything.
I completely disagree. I do not see, in anyway, why the reapers avoiding the citadel would make any more sense with that ending over the current one. If they took the Citadel they could trap humans in their system and be able to harvest them at their leisure.
Sovereign's plan was to take the citadel so the reapers could enter the galaxy. Without him, they had to slowly get out of dark space but once they did, there was no longer an immediate importance to taking the citadel.
The reaper's plan of attack for all the cycles up until now, to the best of our knowledge, hinged on them taking the citadel and trapping us in our own systems. They attacked us system-by-system, one by one. We are stranded and left at their mercy. Personally I still view it significant enough to be called "immediate importance" in that context.
That being said... time is an illusion. The reaper war didn't even last a year. It lasted for a couple months. This is a species that transcends time. To them perhaps a few months IS immediate. They don't have the same standard of measurement of time significance that we do. They've been doing this for a billion years, afterall. In relation to that I imagine a couple months is just a blink of the eye.
So they didn't attack the citadel, because that's where they need to process everyone. Much smarter to wait for all species to evacuate from their respective homeworlds and collect the majority of them on the citadel. Speeds up the reaperifying process.
I don't understand your argument. All of the species to evacuate their homeworlds? The majority going to the citadel? Just how many organics do you think exist in the cycle that the 'majority' could actually be held on the Citadel? The Citadel couldn't come anyway even remotely close to holding our species. Statistically I believe more humans are born every day than there is room on the citadel to hold, even if quarian-conditions. Our entire species could evacuate but theres no way they could all turn to the citadel to house them. Just isn't enough room.
Also Drew Karpyshyn's dark energy plot would contradict Sovereign's speech "we are beyond your comprehension"
If we can understand the Reapers in their actions and motives then that premise is broken.
Proud to say I broke the premise then. 
Anyway that is as far as I'm reading into the topic so some other posts might have addressed these things.