The temple is small, there's two gates and then the main shrine (which consists of the coin-tossing... box and in front is the semi-giant incense pot, the one whose smoke you waft your way)
It's nice, because on most days, it's quite empty. I had more fun going on December 14th, though, as that is the anniversary of the day they attacked Lord Kira to avenge Lord Asano.
Although the temple isn't much to behold, it is historically and emotionally packed. I mean, if you just think, that place is where 46 men took their lives. The ground contains their blood, but also the strength of their will and honor. Therefore, this temple is good to visit, if nothing else to pay homage to these men and burn incense on their behalf. Plus, this story is well-loved by the Japanese people, even becoming a play.
The incense sticks cost 100 yen. The normal procedure is to place a few at each grave, there being so many (there's usually already a pile going, just toss it on top), bow, do your thing.
As for December 14th, typical thoroughfare. What I did find unusual and loved were these 600 yen hamburgers that were GIGANTIC. no picture, very sorry, but they were about the width of a large dinner plate, and stacked to boot. Otherwise, squid, okonomiyaki, taiyaki, creme things, yakisoba, banana sweets; the normal thoroughfare. i think you get charged more in the outside stands so it's better to hop into the inside to look around before buying anything. There's also goods shops (socks, calligraphy, painting, fortune telling, etc.) and the temple's own souvenir shop.
In summary, go to say you've been there. It's like going to Hiroshima, except less historically devastating.
The approach to Sengakuji temple gives it nostalgic charm, but I wouldn't classify it as much more than mildly interesting. It's wedged in between modern houses, sky scrapers and apartment buildings, but it's narrowness makes it an interesting place to take a stroll. Visually, the temple and its grounds are very interesting. The trees around the gate, for instance, are obviously arranged to be part of a visual whole. Several statues also dot the grounds. You can't go into the temple itself: it has tatami floors. Rather, you have to peer in through a rather bleary window. There is also a small graveyard that you can walk through. There, you can buy bundles of incense to place at the foot of gravestones. Outside the temple there are several souvenir stores that cater to visitors.