He's great in whatever he does. Have you seen Terry Pratchetts 'Going Postal'? He puts in a great over the top, panto style performance as the villian while still keeping the character menacing. Totally unrecognisable as the same man who does Poirot.

I fully agree about David Suchet's terrificness (that doesn't seem to be a real word - but I'll stick with it anyways), both portraying the Poirot character and otherwise.