A lot of players have called Sengoku a not-quite-Crusader Kings II: something Paradox released when they didn't quite have CKII's system down, but wanted to make money with something they had thus far. People had told me it was mediocre, and so I wasn't interested in spending too much money on it. Recently it went on sale for $2.70, which is about the same amount of money spent on a few Mountain Dew Kickstarts at 7-11, so I decided to try it out, being a lover of strategy games in general and especially the Sengoku Jidai time period.
So is it true that it's like a poor man's CK2? Actually, there's a LOT of truth in this. Sengoku is basically somewhere between CKI and CKII, with elements from both games in the interface and gameplay. You have your nobles, you marry them, have heirs, interact with nobles above and below you (depending on who you play), and improve the desmense you control directly. Unlike in CKII and later Paradox games, you can't go to war with specific regions as a war goal, but you can capture provinces in a war and keep them as soon as peace is made (a bit like how wars of religion happened in CK1).
Warfare is like any other Paradox game, with individual armies battling it out and battles won/lost depending on a combination of numbers and morale. How the morale is decided, I don't know - sometimes I just throw armies at my enemies and hope the little green bar stops going up and down until I win. The AI does that annoying thing that the AI often did in older Paradox games - namely, refusing to try to stop your armies and just meandering around taking empty provinces, leaving their home country wide open or permitting their armies to be surrounded. In the end, I sometimes fought wars like I was dealing with modern armies - ie., lining up several columns of soldiers and charging into my enemy's territory with a line of forces. If you're looking for a Sengoku Jidai game with detailed individual battles, or campaigns that operate like real campaigns do, you would probably do best to invest in the far superior Shogun 2 Total War (or even its predecessor, which is still one of the best TW games in my opinion).
One of the major hang ups with Sengoku is that, because the war aspect is so limited, you rely heavily on court and political gameplay for entertainment - but this is incredibly lacking. Unlike in CK2 (or even CK1, for that matter), where you could spend half the game wheeling and dealing to work your way up the ranks of medieval royalty and politics, and plenty of events permitted you to interact and make use of your character's personal traits, there is not much of that in Sengoku. Generally, the only interaction I had was having to turn down nobles who kept asking for land and funding my kid's education. I'm sure there are some mods out there that add way more events and make court life as interesting as it was in medieval Japan, but as far as the vanilla game goes, it feels almost unfinished. In the end, it comes across more as a CK2 mod someone made, rather than an actual game created and published onto the market.
Do I recommend this game? This is where I wish Steam had a "maybe" option. I put down "Yes" because the game is fun every now and then, or if you want something CK-ish that is set in medieval Japan...but I would not spend too much money on it. Get it when it goes on sale.