From a playability point of view - this machine is just horrible. I don't like the game much at all. But some say the ruleset is VERY DEEP, and most owners keep their machines, as they are quite difficult. If you want a challenging machine - this is it.
Things to watch out for - I'd say from an Engineering point of view - it is well designed - there's A LOT going on under the bonnet and they are HARD to maintain if they are not reconditioned properly. The cannons are the main problematic aspect of the game. The wire looms wear out over time and give you all sorts of problems. You can have them replaced with a "kit" and just solder them in, or have the looms replaced (wire by wire). The AUX Driver boards (RHS in the head) nearly always have repairs done to them due to a design issue with the Diverter coils and the drop target release coil. You can jump a wire from the drop target to the AUX Driver board. This is covered in Clay's guide.
Ramps - there are three and you will most likely need to replace at least one ramp - or invest in protectors.
Overall - a working and reconditioned ST TNG is a challenging and difficult pin - so it would have lastability in a games room. When they do have issues, they are a bastard to fix.
But there are planty of happy owners who swear by their ST TNG !
