It's a promising movie to watch where there are no major faults in story plot or acting or cinematography. You are kept hooked always by Interesting elements throughout, making the long run-time of 129 minutes easily passed by unnoticed.
Great charisma and chemistry displayed by the two main actors, Ahn Sung Ki and Park Seo Joon. The big generation gap was well handled and they made a believable team to root for.
Really impressed by the funny and warm moments between the Heroes in face of a serious battle against Evil.
Visually appealing overall whereby certain scenes made good impressions but unfortunately, not memorable enough to leave a lasting impact.
If I am to point out any major minus, it would be on lack of narrative of the Villain. Though Woo Do Hwan managed to portray a very sinister and powerful Big Bad character through his acting, his agenda (plot design) is simply not insidious enough to intimidate the audience. This is made worse by how little the interaction time between Villain and the Heroes. In my opinion, if the plot focus more on friction between the two sides instead of the Villain solo act of evil deeds, the result would have been different, a lot!
Summary in one word would be "Harmonious".
With some minor adjustments, it could have been "Awesome".
Thus, I give an additional star for Effort (it should have been 8/10) as I look forward to its sequel.