Not picking through minutia, but here are some highlights. Feel free to copy and past your own additions.
Accomplishments:
Drafted: Dame, CJ, Connaughton, Crabbe, Collins, Simons, Trent (some of these I consider successes because he found NBA talent so late in the draft)
Traded: Plumlee for Nurkic+Pick (that became Collins), Hark/Meyers for Whiteside, Turner for Bazemore
FA Signed: Aminu, Harkless, Hood, Kanter
Let Walk: Batum, Matthews
Big Contracts: Dame, CJ, Nurk
Failures:
Drafted: Leonard (I'm not 100% I even consider this a failure, given it was 11th pick and he is still in the league for legit reasons)
Traded: Barton for Afflalo
FA Signed: Turner
Let Walk: Aldridge, Aminu (he's a talented guy. I was ready to see him go, but he was still a valuable piece.)
Big Contracts: Leonard, Harkless, Turner
Overall he inherited a team that was kind of directionless and floundering with one star player and a decent cast of role players. Adding Dame actually gave us a small chance at championship contention, and when shit hit the fan he executed a full rebuild that had us back in the Western Conference Finals in less than 5 years without dipping into the lottery once.
The lowest point was letting Aldridge walk without compensation. You can chalk that up to LMA weirdness, but when that much talent leaves uncompensated, the GM has to take some blame. Second lowest were the stupid trifecta of contracts in 2016.
His best accomplishments were drafting Dame/CJ (and the jury is out but we may count Simons on that list soon) and locking them up throughout their peak years, and swindling Denver for Nurkic + Pick (that became Collins).
When you look at everything that happened from 2001 to 2012, from the Jail Blazers and Oden Saga and Roy Knee and everything else, it's easy to see now how badly the post-Aldridge era could've gone. It definitely helps that Lillard has led the team through the transition, but hey, our GM is the reason we have Lillard. So if you want to point the finger at Dame, you still have to point the finger at Olshey.
I guess everybody is entitled to their opinions, but given how few free agents Portland traditionally attracts and how we haven't had lots of lottery tanking, I personally don't see how you give him anything less than an A. I kind of waffled on A-, but in the end I think LMA fucks over any other GM in the same situation (see Kwame for example), and everybody was handing out ludicrous deals in 2016. So those failures sucked, but they weren't uniquely sucky.
I probably would've graded him much worse after the Pelicans sweep, and I may grade him differently next year. So there's some recency bias I'll admit to. But jeez, how good do you expect us to be? I feel like some people will only grade him an A if Portland wins a championship. That's too high of a bar, IMO. (Especially given the Warriors Dynasty.) I want a competitive, playoff team with a bright future, and that's what I've got. So I'm comfortable with an A.