I think Cogitative is on the right track in breaking the statement into two parts for simpler analysis, but I'm not sure that I agree with half as much of his or her interpretation half as much as I ought.
My reading of
I don't know half of you half as well as I should like;
is that the speaker is expressing regret that he doesn't know most of his guests a lot better than he does. The other half he either knows well enough (or better than he'd like to) already or wishes that he knew only slightly better than he already does.
As for the second part of the sentence, I think that there are two very different ways to read it. One way to interpret
and I like less than half of you half as well as you deserve.
is expansively, as being directed toward more than half of his guests—those who deserve twice the affection he actually has for them (so that he is implicitly criticizing himself for failing to esteem them as he should). According to this interpretation, the speaker is saying that more than half of his guests deserve to be liked considerably more than (specifically, twice as much as) he likes them. As for the remaining percentage of his guests, he either likes them (or dislikes them) to an appropriate degree, or he fails to like them as much as they deserve but by an amount that is less than twice his current level of affection for them.
Another way to interpret
and I like less than half of you half as well as you deserve.
is narrowly, as being directed only to the "less than half of you" in the room. According to this interpretation, the speaker feels that he likes some proportion (below one-half) of the guests assembled far less than they deserve, but the actual number of guests who fall into that category could be very small indeed; and as for the rest of the guests, this part of the speaker's sentence doesn't address them at all.
No wonder the guests were perplexed by the speaker's remark.