Like Infocom's Nord & Bert, Montfort created an essentially plot free game for Americans with a love for wordplay. Also similar to its predecessor, there is a built-in hint system that will ensure you don't get stuck.
While I adore Ad Verbum, its best puzzle is easily the first one you're likely to encounter, that being the compass rose rooms. The descriptions and responses to valiant attempts to escape these rooms are some of the wittiest I've seen in interactive fiction. I was delighted when trying to leave the south room when (Spoiler - click to show)"skedaddle" worked. I also rather enjoyed the library room. Like others have mentioned, I was disappointed that several puzzles have very little to do with classic wordplay (and aren't terribly interesting), and the Latin pig understands less than he should.