3-D or not 3-D -- that's not even a question as far as Clash of the Titans is concerned.
In the wake of Avatar's phenomenal success, studios are shamelessly slapping the 3-D format onto whatever pictures are in the can, failing to take into account that Avatar's visuals were so stunning because the picture was shot in 3-D. Clash of the Titans represents the laziest use of the process to date: I repeatedly removed my special glasses during the screening and could scarcely tell any difference between 2-D and 3-D. My advice? Avoid any theater charging more to see this in 3-D; it's not worth the extra cash.
As to whether the film itself is worth seeing in any format, that's a closer call. Fans of the 1981 original won't find many improvements here: Ray Harryhausen's lovingly crafted stop-motion effects have been swapped out for the usual CGI sound and fury; the ingratiating sense of camp has been obliterated, replaced by a solemnity signaled by furrowed brows and stone faces (and not just on those who encounter Medusa); and the amusing banter between the gods (played by the likes of Laurence Olivier and Maggie Smith) is noticeably MIA. On its own terms, however, the film is a passable spectacle.
As Perseus, the mortal son of Zeus (Liam Neeson) who must thwart Hades (Ralph Fiennes) by defeating a string of ghastly beasts and saving both a city and its princess (Alexa Davalos), Avatar's Sam Worthington is merely OK (the reason for his high demand continues to elude me), but his character is backed by a colorful assortment of warriors who make his journey memorable. Fiennes' portrayal of Hades may not fall far from the Voldemort tree, but he nevertheless cuts a menacing figure. And while most of the mythical creatures (Medusa, the Kraken) pale next to Harryhausen's achievements, the monstrous scorpions prove to be an exception, and superb FX work allows their battle with the humans to emerge as the film's action highlight.
Those hoping for a Harry Hamlin sighting (he played Perseus in the original) will be left hanging, but rest assured that there's a clever cameo appearance by another vet of the '81 release. It would be cruel and unfair to viewers to ruin the scene here (clue: it involves a non-human character), but it's an amusing gag, and it slices through the rest of the picture's glumness with the precision of a sword crafted by Zeus himself.