Short review *spoilers*
This movie reminded me of Timeline. Except Siyama is extremely watered down and seems to be made for the entire family to enjoy.
A few disclaimers before I continue. I don't claim to have a deep understanding of Thailand's past. Nor do I have a great understanding of weapons in general, medical practices, or time travel.
So the film starts with a huge narrative; basically the "bad" army need to plow through the village of Siyama so that they can meet up with the rest of the army.
Cut to present, and we see 2 girls and a guy driving in a car. Conveniently, one girl is a doctor and is a great archer (bow and arrow). The other girl knows how to throw knives. And the guy is the token buddy comedian who also wears glasses and is nerdy -- he also knows how to "create the greatest weapon ever".
They're driving along, and for no rhyme nor reason, they get teleported back to Siyama. Well, there is some reason -- a monk walking by willed it. So they literally drive right into Siyama, and the guy is already bleeding. They quickly calm down and later that night, they speak with the same monk that teleported them back. The entire time, they've just pretty much accepted the fact that they're stuck in the past. Luckily, the monk says they have so many days before the portal opens up again.
Great, so they spend 2 weeks fighting, plotting, and getting to know each other. We also find out that the main Siyaman warrior is also from the future -- this reveal was entirely too anticlimatic. This is also about the same time when this guy and the archer strike some sort of relationship.
Anyhow, it's day zero when they all finally get to go home, including the main Siyaman warrior. They just drive through the field towards the portal, watching all the other Siyaman warriors get plowed down by the "bad" army. In a sort of cliche way, they don't go through the portal and sort of "emerge" back into the screen. And for some reason, the nerd is wearing his backpack in front rather than in the back.
Long story short, the army retreats, but the main Siyaman warrior and the archer have to jump off a cliff to blow up 2 barrels of TNT so that the rubble can fall onto the retreating army. We don't know what happens to the one girl who's good with knives or the nerd. For all I care, they can stay back in time.
I absolutely had no care for any of these characters. The story and violence was so watered down. The fighting choreography was OK. The CGI was bad. I guess that's the best they could do, considering it was only 100 minutes.
That reminds me; there's a point where the archer/doctor has to remove an arrow from the back of the main Siyaman warrior that's an inch away from his heart. So instead of pulling it out, she pushes it all the way through and pops it out the front. Wonderful. Oh yeah, she of course cut off as much arrow as she could before doing this so he wouldn't have to feel the entire length of the arrow.
One thing that truly bothered me was the movie's lack of worrying about any paradoxes involved in time travel. They introduce a car, new weapons, and the future leader of Thailand. Now, again, I don't have the best understanding of time travel, but I guess these 3 items (may be more) don't really affect Thailand's future.
Anyway, this is a review from an avid American movie watcher. I've seen tons of asian flicks (unfortunately, only a few Thai movies). In general, this isn't the best, but far from being the worst I've seen. Take it for what it's worth. I'm giving this movie a generous 4/10. It's a good way to kill some time.