This is my 2nd 98 GS 400, my 4th Lexus. Absolutely the most car for the money. I highly recommend it. Superior performance, great sound system, quiet ride, and great reliablity and low maintance. The key to Lexus/Toyota is routine maintenance at 30/60/90k/120k miles. My current car has 159k and runs just as well as my last one at 69k. I can't say enough about Lexus quality. Make sure you acquire maintenance records (if it was dealer maintained, any Lexus dealer w/ have the records). This IS a high performance machine, so some people ran them hard. If it was maintained, good records will nullify that. P.S. Get the SRT intake/chip for $300-500 for an added 15-20hp.
Stock stereo has 2 amps and subwoofer (not available w/ navigation in 98, it's one or the other), performance, VSC button allows you to turn off computer controlled skid control (for some fun driving), refined interior and ride.
Transmission is a bit all or nothing, car tends to 'jump' when you hit the gas even moderately (it's 300 hp). Routine maintenance is more expensive than the exact same maintenance on a Toyota vehicle. MAKE SURE THE TIMING BELT WAS DONE AT 90k!