Psych is one of the best show on TV today, and Season 4 is just one great episode after another. The "comfort food" and "no need to revamp a winning formula" comments are pretty spot on, when I think about it, but most of the time I'd be happy to just watch a new Psych that's the same old Psych.
Of course there's more pineapple, and more 80's pop culture references, and more Gus don't be a . . . 's, and more silly aliases for Gus. There are also more 80's guest stars, and of course the Werewolf episode. I liked it so well that I watched the whole season within a week and a half of receiving it. (My 14 yr old daughter kept taking the disc I wanted to watch next, or I'd have probably watched it within a week.) I have most of season 5 on DVR, but still can't wait for it to come out on DVD (and of course for the Season 6 to be aired later this summer).
The gag reel, Psychouts, Montages and deleted scenes are must see.
Haven't checked out the podcast commentaries yet, so I can't comment on those, but although the video commentaries put my wife to sleep, I found them interesting.
Over all I say BUY IT!