We took this tip off an Cambodian expat site (url below for more tips), what a find!!
First impressions are good, a warm welcome and besides us only Japanese eating here. Decor is a nice Japanese style, with normal, and the lower Japanese dining tables.
The food: we ordered Saba Teppan (mackerel), Osaka style omelet with pork & kimchi (a dish you don't see often outside of Japan), Japanese fishcakes, Basho's signature chicken wings and salad. All highly creative and tasty dishes. Including sake beer & water, 25$
Great bargain for brilliant Japanese food!
Note: this place is not easy to find - it's in the Oom Khun Street, just around the corner off Sivatha Rd. look for yellow banners with japanese writing on them, and a porch partly overgrown with ivy (or a tropical lookalike for that matter), it's in the part of Oom Khun that also has the Frangipani Green Garden Hotel in it.
Note II: found more great tips on Siem Reap here: http://www.movetocambodia.com/food/where-to-eat-in-siem-reap/ . Enjoy!