We put in a pool last summer. In-ground, vinyl rectangle, I think 14x30, so medium-sized. 8ft depth in the deep end. We looked at countless options for shapes, but with our backyard being rectangular and wanting to retain lots of area for grass for kids to play on, plus deck, rectangular really did make the most sense. We were $40k, taxes in, and that didn't include the electrical or gas hookups, which ran another $2000 or so. We didn't have many options for material where we live. Most places strongly recommended against concrete because of the winters, saying it's more or less guaranteed to crack within 10 years. Fibreglass was an option, but much more expensive.
Our kids are 6 and 8, so we knew the sooner we did it the more value we'd get out of it. The kids were in it the day it was filled, even before the heater had got it above 60. (filled it with the garden hose - ours and our neighbours, took less than 24 hrs)
I was against it - I didn't think it was worth the cost, even though I know the kids will use it every day, and my wife does laps in it every morning. I still don't think it was worth the cost, compared to what we could have spent the same $$ on - several trips to Europe, Disney, etc. But I can't deny it's a ton of fun and it gets used pretty much every day. And I hear absolutely ZERO complaints about what I spend on the 911 any more
Pic of the installation:
