On Shogun2, definitely worth the price especially when it is so cheap, though you would wanna consider if you want the pointy sticks men (Shogun 2) or smoking guns men more (Shogun 2: Fall of the Samurai). I personally enjoy melee more than rifles but both are great games from the Total War series.

Bout comparing it to Civ5, I don't think it is anything similar to Civ5. Shogun 2 is more on battle where you spend most of the time besieging or defending yourself against the tide of ashigaru/samurais with a general building and tech trees to develop the provinces for more tax/advanced troops. Civ5 is more on building and managing an empire/dynasty/nation that will last the ages whether in military might, cultural influences, science, etc. You also go to war in Civ5 but it is just a part of overall Civ5, and there are plenty more (e.g. go full nerd on science pump or spamming culture all over) than just sending units against another civilization.

If you enjoy leading troops in battle and planning tactical maneuvers etc with simplistic building/tech trees, then Shogun 2 all the way.
If you enjoy building up cities, managing the empire, simple (though sometimes repetitive) battles, choosing different ways of dominating/winning instead of pure brute force all the time, Civilization 5 all the way.

I gotten both and I love 'em both. If only we can mix both together well enough (RoTK comes to mind but not in-depth enough).