First Installment Wins: Although it is not considered anymore the uber-hit which was hailed up as at his day, Ong-Bak is still seen as the best of the trilogy, one of the best films of its generation, and pretty much the only work by Tony Jaa which is not considered unsatisfactory or suffering from Sequelitis in any grade.
Follow the Leader: The film was a refreshing work with a young new name in a film genre increasingly populated by aging stars, and marked a new direction with elements like wireless stunts, nonstop pacing and cringe-inducing hard fight scenes. Even Donnie Yen would admit he used the film as a motivating force behind his own late career.
In the first movie, a horribly battered Humlae shielding Ong-Bak with his body when Komtuan tries to smash it with a hammer - and then keeps shielding the statue while the crime lord keeps beating on him. For a character as selfish as Humlae has been throughout the movie, that is saying something.
Tony Jaa lights his legs on fire and kicks someone in the face!
"Seinfeld" Is Unfunny: With its intense action and colourful quirks, Ong-Bak paved a new way in the martial arts cinema and managed to stay high for many years, helped by its sister film Tom-Yum-Goong and its Up to Eleven action. However, after films like Merantau and Ip Man surfaced on its wake, people realized that martial arts films of the same caliber could be worked out with actual plots and drama beyond the typical action flick Excuse Plot, and their opinion Ong-Bak became tepid over the years (although it is still considered an undisputed classic).
Signature Scene: The scene where Ting fights 3 fighters in a row in the underground fight club is this for the first film. While the film has a number of spectacular scenes, this one tends to be most remembered by fans.
Ass Pull: Bhuti appears from nowhere to cause Tien's defeat, and it is not until the sequel that it is explained (barely) who he was. This is actually a sign of the terrible production of the sequels, as he was introduced very late in the script in midst of chaotic rewrites.
Moment of Awesome: Tien's fight against the brotherhood of bandits/pirates/ninjas that adopted him and taught him every form of combat known to man. It's a bit of a marathon too, and many viewers will be exhausted by the halfway point.
Admit it, you laughed in the third film when Rajasena's severed head began to talk.
Also in the third film, Ping insistently singing some ritual song while helping unsuccesfully a crippled Tien to rise to his feet can become rather cheesy for the viewer.
Sequelitis: While Ong-Bak was universally liked at its time, the sequel was pretty divisive about whether it successfully lived up to the Tough Act to Follow or it was too outlandish and pretentious. For its part, the third film was unanimously disliked by the fans, who spoke against the unexpected inclusion of supernatural elements and the overtly mystic and sometimes bizarre plot developments.