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It’s not always easy being big and green on the silver screen–just ask Hulk–but Shrek, as it turns out, carries it off spectacularly not once but twice. DreamWorks’ sequel to its 2001 computer-generated smash is the rare followup that matches its predecessor. Bright, witty and very nearly without a dull patch, “Shrek 2” should, once more, delight youngsters, teens and those above voting age in approximately equal measure. In the process, it will undoubtedly take in an enormous haul of green of yet another sort, and deservedly so.

The plot devised by director Andrew Adamson, Joe Stillman (a co-writer of the original), J. David Stem and David N. Weiss is a very simple one. The king (John Cleese), Princess Fiona’s (Cameron Diaz) father, is aghast at her marriage to Shrek (Mike Myers), especially since he had an arrangement with the ever-ambitious Fairy Godmother (Jennifer Saunders) that the princess would wed her preening son Prince Charming (Rupert Everett). Unknown to his wife the queen (Julie Andrews), he engages a supposedly deadly assassin, Puss in Boots (Antonio Banderas), to do Shrek in, but the cat instead falls in with Shrek and his Donkey buddy (Eddie Murphy), and they go off unsuspectingly to seek the Godmother’s help. Mistaken identities abound when Shrek and Donkey are magically transformed into a handsome human and a prize-caliber stallion, while Fiona comes to believe that Charming is the new Shrek. The big finale has Shrek trying to bust into a royal party where Fiona and Charming are celebrating “their” nuptials and reach his wife before midnight–by which time he has to kiss his bride to make his new body permanent (and keep Charming from kissing her and magically cementing their love).

This scenario, of course, is just a skeleton on which to hang a succession of clever, amusing episodes that allow for the same sort of sharp jabs at the conventions of the fairy-tale that marked the first picture. Like the original, “Shrek 2” takes special pleasure in mocking the sort of sweet, misty-eyed stuff that marked Disney animation for so long, and it also takes a few specific anti-Disney potshots: Ariel makes a fleeting, and none too happily-ever-after, appearance, for example, and the whole Fairy Godmother business (with the character looking a lot like Shelley Winters, of all people), brings back (and twists) plenty of memories. It also takes the obligatory post-modernist route of inserting jocular references to other movies (one relating to “Mission Impossible,” for instance) and television shows (the “Rawhide” theme is heard at one point, and there’s a great takeoff on “Cops” called “Knights”). But most of the gags that the picture offers come from its own demented sense of humor rather than any direct slams at other pictures. It brings back Murphy’s fast-talking Donkey, who once again proves the actor’s best role in years, as well as other characters from the enchanted forest where Shrek lives (Pinocchio, the three blind mice, and others) to good effect, and gives them all generally winning material. By far the best supporting player, though, is the new one: Puss in Boots, in whom the disparity between physical reality and pretension to grandeur could hardly be greater. It’s a great character, wonderfully rendered (the shots in which he plays the pleading-eyed kitty are wonderful), and Banderas seizes the vocal opportunities it affords with real panache. The picture’s a visual treat as well, with plenty of good sight gags (the entrance into Far Far Away, as the king’s kingdom is called–which looks suspiciously like Hollywood–offers plenty of them).

Of course, not everything works equally well. Cleese and Andrews are shortchanged; most of the stuff dealing with the king and queen, save for a dinner sequence and a final twist, is fairly flat, and the running-time dealing with the Godmother and Charming isn’t terribly strong, either. There are also a couple of unnecessary examples of gross-out humor (mild, to be sure, but still dispensable).

But one can easily forgive the missteps in view of the many joys “Shrek 2” has to offer. This is a charming, funny sequel which can’t match the original’s sense of freshness but makes up for it in style and good spirits. Incidentally, it’s one of those pictures, like “Ferris Bueller,” that has a surprise awaiting viewers after the final credits. If you don’t want to miss a good concluding gag, resist the urge to bolt out as the names begin to roll and sit through the crawls.