I almost bought an IS250 but in the end purchased a 2010 Audi TT TDi Quattro, so maybe I can add some insight. My recent car history includes an e92 BMW 325i, an Audi a4 1.4Tfsi, and Audi A6 45TFSI Quattro. Post pandemic I decided to downsize to a cheaper, older car even though I'm still doing about 10,000 miles per year.
I test drove a couple of IS250s and was impressed in many ways. The interior is beautifully made and has lots of toys, the car looks great from the back and side and it cruises down the road in comfort and relative silence. Against that the front of the car looks dated, the engine, while smooth, is noticeably less accelerative and much more thirsty than my Audi diesel engine, there's a slight hint of being underbraked (not too bad though), it's more of a cruiser than a sporty handler in relative terms and the back seats are tiny and don't fold down.
Also, in financial terms, the road tax is much more than the Audi TT, the fuel consumption is much greater, it's fiddly having to buy E5 petrol and, surprisingly, my insurance quote was quite a bit higher. Admittedly the back seats in my TT are even tinier than the IS250 but they do fold down and allow me to get a bicycle into the rear hatch.
I'm not suggesting that many will cross shop an IS250 against an Audi TT as they're completely different cars in many ways. I just felt that the Audi TT was more contemporary in terms of its looks, handling, braking and performance/fuel economy trade-off. It's nowhere near as luxurious as the IS250 and I completely understand why many love the IS250. But in the current financial climate the IS250 is turning into a more costly proposition in routine running costs, somewhat offset by its excellent reliability.
