This isn't the worst Diabelli Variations I've ever heard (it's better than the atrocious Barenboim Erato recording), nor is it even especially bad. However if you place it side by side with the Brendel, for example, it seriously lacks in some places. Pollini approaches the music in an almost mechanical way, giving us nothing more (and nothing less) than the notes on the page. Maybe some people like this kind of objective approach, but in this case it falls flat because it fails to convey the sly humour in many of the variations.
Having said that, Pollini polished virtuosity gives him the edge over Brendel in the faster variations (and his account of Vars 31-33 is definitely a keeper) but he is painfully unexpressive in the earlier slow variations.
Fortunately, the ability to create our own playlists means we can create our own 'ideal' Diabelli Variations from all the recordings out there. If you're one of the people who do this, I can suggest this disc for Vars 31-33, 27-28 and 9.