So I've played through ME2 a couple times and almost got through a third playthrough before stopping myself short.  I decided I want one last playthrough to be my definitive save game and I'll do all the DLC on it and make all the decisions I want to make.  Maybe I'll want to come back to the game again later, but I doubt it'll be before 3 is out.   I've beaten the game on normal and veteran with an infiltrator and a vanguard, and beat it most of the way with a soldier on hardcore before deciding I didn't want him to be my main guy.  I also played a little insane with the infiltrator, but while I progressed, I found it frustrating enough to wonder whether I want to play through everything at that difficulty, especially some of the harder encounters I hadn't gotten to yet (collector missions mostly).  What is the perfect difficulty/class combination for a complete playthrough for you?  I appreciate your suggestions.

I've played once through ME2 and that was only with Zaeed DLC. I've gathered the rest of the DLC so far for one big playthrough (except most of those ugly helmet collections) and I'm planning on going through ME1 as a Soldier and carrying that onto ME2 and staying as a Soldier (I see that to be my true class for Shepard).

I've been putting this off in case of pre-suicide mission DLC, but we pretty much know that all that is left is a bridging expansion. 
 
Difficulty doesn't really matter to me, but I'm going through ME1 on an easier setting to quicken things up but will go for insanity on ME2 because I haven't tried that out. The first time I play through a decision heavy game like Mass Effect is better because I play it as I would, then I get all obsessive for the definitive one.

(Spoliers ahead)
I've played through ME2 with Jacob and Jack, my only non loyal characters, dead and all of my crew alive. Luckily I hated the two :)
 
I don't really see a point in "perfecting" your Shepard; it was a suicide mission, it was clear someone would die. And playing through the ending more
than a few times seems a little bit like cheating to me (NOT playing through the game multiple times - just the suicide mission - I'm all right with that).

My first playthrough is my definitive playthrough. I've done every quest there is in the game, including all the DLC, I didn't look on the internet on how to survive, everyone was loyal and they survived, is it really hard to keep everyone alive?
 
I played a soldier and I'm lvl 30, played a female Paragon
 
I finally started my second playthrough a couple of days ago, female renegade on Insanity......the name fits because it drives me insane sometimes

 I was a soldier in ME1 but that was boring as shit so I replayed that as an adept and it was way more fun, then I did it in hard and then insane. In ME 2 its not quite as fun to be an adept but on insane which I am playing through now as a renegade its not that hard either. I have never even touch any of the other classes but I might go for a soldier run in ME2 before ME3 comes out. Although the adept Shepard  is the one I will properly take through to ME 3.    I lost Mordin on my first play through but I just loaded it back and re did it because it felt a little unfair and because I liked Mordin. 

I blazed through ME2 after buying it during Steam's holiday sale.  I sold the Geth team member when given the chance, delayed saving the Normandy crew to finish one last Loyalty mission, then hopped through the Omega 4 Relay.  In the end, half my crew died.  My entire team survived, though.   
 
I have started a new file that carries over my ME1 character, but I can't really call it a definitive run.  I have yet to buy the Kasumi, Overlord, or LotSB packs.  I'll probably do that around the time I buy ME3.  As for difficulty, I gave Insanity a try, but quickly grew annoyed at the fact that I might as well not have had any shields.  For now, I've settled on Veteran.

" (Spoliers ahead) I've played through ME2 with Jacob and Jack, my only non loyal characters, dead and all of my crew alive. Luckily I hated the two :)  I don't really see a point in "perfecting" your Shepard; it was a suicide mission, it was clear someone would die. And playing through the ending more than a few times seems a little bit like cheating to me (NOT playing through the game multiple times - just the suicide mission - I'm all right with that). "