I worked on VW's for a while, and a Mk IV can be a fun car to drive, but not so much to own. The good thing is that, by now, many of the things that plagued them while they were still fresh have now been fixed, mostly via update parts. Think window regulators, coils/coil packs, catalytic converters, even just the ECM programming on many models has by now been made useable.
Parts can be expensive to people used to American or Japanese makes in many cases, and except for the 2.0 engine, they require good oils etc and a somewhat excessive amount of babysitting compared to their main competitors. But if the owner is willing to go the extra mile (to the dealer parts counter most likely) a Mk IV can be a fun car to drive. I frankly always had a smile on my face while driving one of most any variety, even a 2.slow. Good powertrain combinations are the 2001-up 1.8t 5 speed manual, 2003-4 (NOT 2002) 1.8t 5 speed automatics (it's a Jatco!), 2002+ VR6/any trans, 2001+ 2.0/any trans, any/TDI/any.
Still, I'd want to see a stack of receipts and paperwork with a used Mk IV, and absent that, I wouldn't touch one with the proverbial 10 foot pole.