Here is a sampling of what they had to say:
Eric Grode in his Broadway.com Review: "The killer rabbit makes an appearance in Spamalot, along with the flatulent Frenchman and the head-banging monks. But something is missing from this frequently enjoyable, relentlessly on-message conflation of Monty Python shtick with Broadway razzmatazz. The blend of star appeal, Python pedigree and a handful of decent gags might well be enough to make Spamalot a runaway hit... That alchemic combination of old material and new stagecraft, however, rarely takes place. The beloved Python routines are performed with relish but little in the way of fresh insight. Most surprisingly, many of the new jokes feel like placeholders."
Ben Brantley of The New York Times: "It is possible for theatergoers who are not Python devotees to enjoy themselves at Spamalot… It would seem unchivalrous not to share in at least some of the pleasure that is being experienced by a cast that includes Tim Curry, Hank Azaria, David Hyde Pierce and a toothsome devourer of scenery named Sara Ramirez. Still, the uninitiated may be bewildered when laughs arrive even before a scene gets under way…The vignettes lifted straight from the movie have an ersatz quality, in the way of secondhand jokes that are funnier in their original context. Broadway performance demands an exaggeration that doesn't always jibe with the unblinking earnestness of the Python style… That Spamalot is the best new musical to open on Broadway this season is inarguable, but that's not saying much. The show is amusing, agreeable, forgettable—a better-than-usual embodiment of the musical for theatergoers who just want to be reminded now and then of a few of their favorite things."
Howard Kissel of The New York Daily News: "Perhaps if I didn't know their sketches by heart, I might have been more charmed by this incarnation... It is amazing that Mike Nichols, who directed the production, and his crew have found so many ways to create stage approximations of what was clearly conceived for film... But all too often I was reminded of Mamma Mia!--the Python fans around me greeted familiar routines the way the Mamma Mia! audience laughed when it recognized the ABBA songs in their new context... Moreover, although the dialogue from the movie like a debate about the ability of a swallow to carry a coconut, or the taunting of the nasty French person remains delicious, the new material is less impressive--especially the songs, with lyrics by Idle and music by Idle and John Du Prez... I could admire all the affection and ingenuity that went into adapting Spamalot to the stage as well as the Herculean energy the cast puts into it. I only wish I had laughed more."
David Rooney of Variety: "The show is an even more episodic patchwork than the British comedy team's movies, but the irreverent Arthurian romp's brash, lunatic spirit is impossible to ignore and almost as hard to resist…. Fact that the show is more memorable on a scene-by-scene basis than as a somewhat forced package will matter little. With the expert manipulation of director Mike Nichols and a cast riding high—a little too high at times—on infectious enjoyment, Monty Python alumnus Eric Idle and co-composer John Du Prez deliver a rowdy entertainment that remains sufficiently faithful to its source, Monty Python and the Holy Grail, to satisfy nostalgic fans, while broadening the humor to cast a wider net among musical theatergoers."
Michael Kuchwara of The Associated Press: "Its authors have had to walk a precarious line--pleasing those fanatical Python fans who have committed the entire movie script to memory while satisfying other theatergoers who never have heard of the Killer Rabbit… To fill out the story, Idle has added a new plot, in which Arthur and his knights must perform that most daunting of tasks—bringing a musical to Broadway… The attempt is similar to what Gerard Alessandrini has been doing so well off-Broadway for more than two decades with his Forbidden Broadway revues. Only Spamalot does it on a much more lavish scale—and with middling' success."
Elysa Gardner of USA Today: "Idle approaches his subjects with the cool and sometimes snooty detachment of a deliberate outsider. A diva-like figure called the Lady of the Lake, played by the aggressively hyped Sara Ramirez, is inserted into the plot as a construct to send up all things banal and excessive about middlebrow entertainment. By the time Ramirez has scatted and slithered through her third overblown number, the joke has been stretched as thin as the costumes that Tim Hatley paints on her buxom figure. Spamalot is much more inspired when it sticks to the kind of droll characters and wry pranks that made Python an institution… An excellent supporting cast helps ensure that Spamalot has the kind of egalitarian appeal that the founder of the Round Table would have approved of—which should be good news for the real-life producers banking on the show's long-term prospects."
Gordon Cox of Newsday: "Eric Idle and Mike Nichols have indeed fashioned a Holy Grail of a big, crowd-pleasing Broadway musical comedy out of the 1975 cult film Monty Python and the Holy Grail. The show slays 'em like Excalibur. Monty Python's Spamalot is so polished and user-friendly, in fact, that those whose adolescences were irreparably warped by The Holy Grail—and we know who we are—will miss the low-budget flick's spiky, unapologetic anarchy.... Under the assured, regally goofy direction of Nichols, the all-star team of David Hyde Pierce Frasier, Hank Azaria The Simpsons and Tim Curry The Rocky Horror Picture Show have an obvious blast... The breakout in this boys' club, though, proves to be the show's leading lady, Sara Ramirez."