Greville was a moderate reactionary and a lot of his views look silly in retrospect - he hung out with people who thought that the very minor reforms of the first Reform Bill (some extension of the franchise: abolition of parliamentary constituencies with no inhabitants) would lead to chaos, mayhem and Republic. He is very silly and unpleasant indeed on the abolition of slavery in the West Indies.
On the other hand, not being a Victorian, he is sensible about some things like the project of converting India to Christianity.
Some things he gets right - he sees Disraeli as a player from his first emergence, and he appreciates the importance of technology. He also moves back and forth in his opinion of people, basically admiring the Duke of Wellington and the young Victoria, say, but expressing considerable irritation with both of them on a day to day basis.
Interestingly, without saying so quite in clear, he clearly believed that somehow Wellington had been responsible for the death of Huskisson, the Chancellor of the Exchequer, who was the first human being ever to fall under a train. Huskisson was Wellington's enemy and an inconvenience and got himself trapped and confused on the line on the occasion of the opening of the first railway. Wellington extended a hand and Huskisson stumbled up the track towards him, thus fatally delaying getting out of the way. Was Wellington capable of cold-blooded murder? Undoubtedly. Was Huskisson's death in his interest? Certainly.
I quite like the idea of the great general also committing something like the perfect murder...
A lot of the issues Greville regards as crucial on the day he writes about them are things we have entirely forgotten about and which he does not regard as less important than things which go on mattering, like the Irish potato famine.
I suppose that a hundred and seventy five years will sort out our preoccupations interestingly.