ME2's main plot wouldn't have been any better if it was more fleshed out. It's a pointless sideplot that goes nowhere. From the reaper POV it is needlessly risky and with little gains, because what, they make a new reaper? So fucking what? In the first game, Sovereign needed a giant fleet of geth and agents inside the Citadel in a sneak attack to be able to break through to the center of the Citadel and maybe win. The collectors have maybe 3 ships total. Oh and the collectors wanted to invade Earth with that. Also they kidnap people from unguarded planets. The moment a little bit of resistance showed, aka 3 turrets and Shepard and his 2 buddies on foot, they ran the fuck away. Like you said, there are isolated elements that could be intruiging, but as a single story it's laughable.
I already described how ME3's main story is bad from the word go in the spoiler tag. The entire setup for it however, is genious. Genious how it negates literally anything that happened in the first 2 games, because the reapers can just show up. In 6 months, they went from being outside the milky way, to invading Earth. Why the fuck they didn't do that to begin with, will not be explained. Btw, bonus points if your remember the plot of the first game. Where they are stuck outside and need the Citadel, a giant mass relay, to be activated or they're fucked and can't do anything. Whoops.
Suicide mission is the most overrated mission in games btw, it's novel the first time around, but then you realise it's basically a Telltale game as far as choice and consequences go. Incredibly linear and funneled. For example, if you pick the wrong guy to go in the vents, what happens? They die! But how? Well, you'd expect their skillset to be insufficient and they die due to that? Fuck no, they do just fine, but at the very end of the sequence, when they have to close a door, they just happen to look outside for a second and get shot in the head. Lol. If you picked the wrong guy to lead the first team, he gets shot and dies at the afformentioned door. But the leader gets shot either way. Only if you made the correct choice, then they brush it off and you pat them on the shoulder. Lol.
Kai Leng is inexcusable. Design wise he's a Deus Ex reboot ripoff.