Thank-you for your comments cyclops. It's fun to read some kyu thoughts on the game : )
24: S4 is the correct shape move here, you could say it's similar to these shapes:
34: O6 is critical for limiting Black's potential by giving White presence farther to the left and pressure on Black's unfinished shapes.
Since Black's moyo is limited and Black needs to maintain a territorial balance with White's solid territory, Black takes the top-left with 35-43 and the top-right with 47 while keeping small moyo potentials around the board. By move 54 and 56 White is induced to reduce Black. Black's game hinges on gaining points from attacking White's reducing groups and hoping his unfinished shapes aren't serious enough to leave him behind on territory after the fighting has settled.
52: Yes, L+1 lives or dies with sente. However the top-left has B19, so it's no longer such an L+1 shape.
I didn't know R12 was joseki : )
56: Perhaps it's sente, but is it larger than Black solidifying the moyo on the left? Sometimes we're willing to take a loss when a move at another part of the board compensates for it.
70: We can see that because of all the unsettled groups and unfinished center-facing shapes that the center is becoming quite valuable. Gaining moves in the center would be more valuable than second line stones on the side. If White plays 70 at B12, then after Black strengthens in the center he could play B11 and split White; and if White follows up with B11 to prevent this, we can say that a stone at B11 would be less valuable than an additional center stone, where all the action is. Therefore, playing the D12-B12 exchange is correct here. The D12 stone also has potential follow ups to keep Black unsettled, and it will be a long time until capturing the single stone of D12 will be more valuable than any other point on the board.
76: It's important for White to split the left group from the right and bottom groups from the direction of the center, because this is where the majority of Black's shape defects are.
If White tries to separate the right side now, then Black is able to play and strengthen the center first. White is unable to effectively cut Black's center groups after this, because White has her own weak group of N14 to handle. White loses her chance to exploit Black's center defects.
84: White is connecting her groups and separating Black's. If Black submits to living quietly, then it will be cramped while giving White plenty of center stones. These new, White stones can be used to split and attack the right side. Eventually, the fight will drag towards the bottom where the majority of Black's weaknesses are. It's a poor strategy for Black, so instead of living passively Black 85 is at J13 -- and rest of the game unfolds from there.
86: If G6 were the only weakpoint on the board, then it could be a nice move to play. But since there are other weak groups and points, then it's better to drag fighting into the weak points. The opponent's position will collapse naturally.