'Honten' means 'main store' or 'original store' - if a restaurant spawns a chain, they'll refer to the first one as the honten. Maybe you could call it the 'flagship', but for some chains the original store is smaller and less glamorous, and they preserve it for historical reasons. The funny thing about Imaiya Honten is that Honten seems to be part of the name - every one of their branches is a flagship.
Now, they do have a fancy style going on for a chicken shop. Between the front door with the flowers, and this neat cave-like style (where we didn't get to sit because it was too smoky), it has the hallmarks of a place that's positioning themselves at the higher end of the casual dining segment.
Chicken places usually aren't great drinking place - if anything they serve a lot of distilled liquor (shochu). Imaiya has shochu, but also has a really distinguished selection of sake - enough so that you could go there for the nihonshu alone. There were a good 20 on the main list, including good brands at good levels as well as smaller things (like Akita's Azakura), and then there was a list of 10 specials including a bunch of summer items. The serving style is nice - pretty glasses, and these cool round masu that they fill to overflowing. Really overflowing - both times she tried, the waitress spilled a lot, got a towel to wipe it up, spilled and wiped some more, and finally got everything overflowingly-full. That probably wasn't in the training manual.
The food is unfortunately a bit ordinary considering what's gone before. We had a round each of some of the standard yakitori items; you'll recognize the negima, and bonjiri and tsukune in the pictures. What's a bit less ordinary is the miso-topped kiritanpo (bottom middle); these are a standard item in Akita, where the sticky rice is squeezed onto sticks and grilled before being cut up in stews. Here, the rice was pale, the miso flaccid, and the overall effect, well, sucky. Too bad. The big grilled chicken breast, a specialty of the store, was quite good, especially the skin as is obvious from the picture.
My colleague's first reaction to hearing the name 'Imaiya Honten' was "It's a bit expensive, isn't it?" and this is true. When we left, far from full, to go to another place, we were genuinely surprised at how big the bill was. If you went, you'd want to go in with a plan, then order carefully and mind your stops and limits. But you could certainly have some fun with the drinks (and the hilarious pouring, if you got the right waitress).