Having played both Nobunaga's Ambition 12 (Kakushin) and Nobunaga's Ambition 13 (Tendou) on my PC, with all the patches and PUKs available, I'd advise against it.
Yes, these were the Japanese version, I imported them and with a little tweaking to handle the Japanese characters, they are very playable. So, I am one of the very few.
While the games are gorgeous, the orchestrated music is extraordinary, and the features interesting and even innovative, there are gaping balance problems that ruin the whole show down the drain. Namely, the Takeda retainers are insanely overpowered. It swallows the competition every single time within 30 years because they have a strong starting base (4 castles in Kakushin), and a stack of unbelievably strong leaders compared to those who should be holding them back, the Uesugi and the Hojo. So as soon as they grow, they are a unstoppable steamroller.
Just to tell you, 99% of the time I've seen the Hojô clan annihilated by the Takeda without the Uesugi lifting a finger. In itself, this is so, so wrong, as these three had an "understanding", a chivalrous triangular policy of balance of power between these three to stop the others from expanding.
That would be fine if there was some limiting factor to the number of troops one could hold, pay, and feed, like in past iterations. However, there are nothing of such. Rice is only used when troops leave the castle. When in castle, you can just hoard troops and rice without the latter limit the former.
So the Takeda, with tons of troops and unspeakably inhumanly strong leaders, squash the competition every time, even the Uesugi which, even with a strong leader like Uesugi Kenshin, cannot follow suit against the Takeda.
As for diplomacy, it is theorically possible to create a coalition against such a power, but against the Takeda this coalition just isn't strong enough and they end up swallowed into the Takeda domain.
Nobunaga's Ambition 11 (Tenka Sousei), however, is another matter. This is easily one of the best balanced NA game since Lord of Darkness, and it is slightly more politlcal. Diplomacy is spot on, with power blocks allying and plotting against each other. The AI's expansion is reasonable, and more importantly there is only so much troops you can hire, which forces you to seek alliances and improve your leaders through training or items to compensate for a limited host of soldiers.
In Tenka Sousei, I've seen Takeda Shingen die around its estimated death year with a domain more or less the same size as in real life, and then quickly crumble in succession wars, which was satisfying in itself compared to the Kakushin steamroller.
However, I agree battles can be a bit underwhelming compared to Kakushin/Tendou, or even Takeda 3. It is the last NA game with a two-step out-of-map battle system, with units in which 1 tiny soldier represents 20 soldiers. Allies included, the two sides can only field a max of 8 commanders + 4 allies commanders each, which may seem tiny. However, it precludes any steamroller advantage from occuring (unless attritional) because there are so much soldiers you can use in a single battle.
If I had to tell you which Nobunaga's Ambition you should play, it would be Lord of Darkness on the SNES or Tenka Sousei on the PC (with the PUK). Sadly, I know of no Japanese/English patch, so I use my knowledge of the PS2 game and my kanji dictionary to translate it for myself.