There are a couple of things to remember when watching a movie like The Smurfs. One: rarely do films measure up to the cartoons of yesteryear; it would be unwise to expect such. Two: the phenomenon of interpersonal communication known as language will be compromised by excessive use of the word "Smurf" as both a noun and a verb, among other grammatical functions. It's probably better to just go with it.
Scooby-Doo director Raja Gosnell appears to have adopted this philosophy -- that is, of not thinking too hard -- in the making of The Smurfs, along with the cast (Neil Patrick Harris in the role of an anxious, fledging businessman and Jayma Mays as his kindhearted, pregnant wife). At one point, Harris asks the Smurfs how they get their personality-based names; for example, does Clumsy Smurf become Clumsy Smurf upon his birth, or only after he has proved to be clumsy in life? The Smurfs' answer is, simply, "yes." Even Gargamel (played by Hank Azaria) sarcastically references a piece of Smurf history (Papa Smurf is apparently the father of 17 sons and 1 daughter) as "not weird at all."
This element of self-awareness, while heavy-handed, manages to save the film from itself. Taken seriously, The Smurfs is a bad movie. Taken as a lighthearted summer flick that everyone knows doesn't match up to the magic of a Saturday morning in the early '80s, it's a passable, albeit totally forgettable, experience.
The premise is a flip-and-reverse of traditional fantasy conventions: rather than a child stumbling upon a strange and fantastical world of magic and mythical beasts, a group of Smurfs (Papa, Clumsy, Brainy, Grouchy, Gutsy, and Smurfette) are whisked, via portal, to New York City, where they stumble upon two unsuspecting and entirely non-magical adults (Harris, Mays). Unfortunately, Gargamel has followed them; he promptly sets up shop in a famous New York landmark without setting off any alarms, and does his best to hunt down the Smurfs. His goal is to capture their "essence" through snips of hair (a similar soul-sucking motif can be seen to much better effect in Jim Henson's 1982 fantasy The Dark Crystal), increasing his own power by doing so. The Smurfs find an unlikely friend in Patrick Winslow (Neil Patrick Harris), who turns out to need encouragement of the Smurfy variety to make an ad campaign (the image for which he pulls from Wikipedia) successful.
The film plays like an infomercial for New York tourism, stopping at Central Park, Belvedere Castle, Time Square, FAO Schwartz -- pretty much anywhere and everywhere a Smurf could run amok. The voice work for the Smurfs themselves, aside from George Lopez's pitch-perfect Grouchy Smurf, is relatively unremarkable. Azaria is, for the most part, everything one would expect Gargamel to be, though at times he goes way over the top -- saying, doing, and experiencing things (like getting hit by a bus) that really only work for actual cartoon villains. Harris and Mays are fine in their roles (neither of which, particularly Mays', is too much of a stretch from their incarnations on Glee); however, the movie, having been made essentially for children, may have benefitted had one of the human leads been a child.
There's nothing particularly bad about The Smurfs, length-wise, plot-wise, or otherwise. The problem is that there isn't anything particularly good, either. As mentioned, the film is bolstered by a sense of its own silliness, but one still gets the feeling that no one involved with this project really tried. Ironically, Harris' character struggles with whether or not to make a safe choice, career-wise, or go with a riskier decision that his heart of hearts yearns for him to take. It's doubtful that The Smurfs would have been great in anybody's hands, but being safe as opposed to terrible does not a good movie make.