Finished ME2 Legendary on Insanity, final playtime about 17 hours with every squadmate surviving the final mission. Like I mentioned previously, the issue with the Insanity difficulty is that it starts at maximum, and therefore basically plateaus from the word go. As such, depending how you look at it, there either is no difficulty curve whatsoever, or there is one - downwards. But I imagine the class choice is actually what makes the biggest difference on Insanity. The Mattock + Adrenaline Rush combo with the Soldier's access to ammo types is so preposterously OP that it almost feels like a cheat code. In the final mission the collectors just melted before my eyes, and I trounced the final boss in like a minute. Whereas playing the Sentinel class on Hardcore I remember the Vorcha on Omega proving a massive difficulty spike due to their regeneration.
Ultimately Insanity felt a bit tedious to play, because the solution to every situation was always the same: take Miranda because she has both Warp and Overload, spam Adrenaline Rush like there's no tomorrow, and use Barrier as a panic button for instant shield recovery. The Arc Thrower was also incredibly vital, because it could hit enemies behind cover, and stun entire groups at once. There weren't many situations where I felt I needed any significant switchup in approach, except for one specific enemy: Husks. On Insanity they become one of the most dangerous enemies in the game because they all gain a layer of armor, and can swarm you in seconds if you're now careful. But sections where that becomes central can be counted on like on hand across the entire game, so it's not a big deal. Using Inferno Ammo to first strip them of their armor, and using Thane's Throw Field to instakill entire groups at once was quite tactically satisfying.
Anyway, on to ME3 on Insanity in the near future. It's what I'm most curious about, because even on Normal you can die pretty damn quickly, so maybe it'll finally put my 1337 hax0r skills to the test.