I'm assuming its your in-law's car so a plus is that you know the history of this car versus the many E46's which are now on their 4th or 5th owner. That being said the worst thing for these cars it to let them sit, but doesn't look too bad from the photos though, however a good PPI can go a long way.
As long as the engine and cooling system are pretty good, along with the rear subframe, then you should be good to go outside of cosmetics. Car will undoubtedly be leaking oil (its not a BMW if it doesn't
) Hopefully no coolant issues though or cracked plastics under the hood from sitting. 115k on the dash as well isn't bad, I took my 330i to 200k+ miles before the cooling system had a meltdown, and my son's X3 3.0i is sitting pretty at 168k (although was meticulously kept after by the original owner).
The only downside I see with the car is that its an auto. As a fun weekend car, a manual E46 (or other manual BMW of that era) would be a lot more fun and desirable but manual swaps are very common as well and could greatly improve the experience. That being said, the overall platform is still great in all forms, you get a much lighter weight vehicle, the fantastic naturally-aspirated M54 engine, as well as beautifully communicative BMW hydraulic steering (RIP) and timeless design inside and out. Worse comes to worse you sell it for parts.