I am a Haunted House owner, and did many things to make it feel like ''okay, it's ready for prime time play''
First thing to know is, you need to do certain things to make sure you can play it more than taking the glass off. Many people in general are put off by system 80, because they do quirky things that other pins are not so inclined to do. Once you get a solid feel for system 80, it's like making your way around your kitchen.
Haunted House really isn't much different than other system 80's, if you follow these rules, you should be pretty good.
One: inspect all the connectors carefully. Sometimes the connectors will look good inside their harness, yet you will have things on your game not work. This is because the pins lose their tension. Buying replacement pins is cheap, and doing the work is easy (but tedious) Good connectors are half your battle with system 80 imho. Aj6 is almost always a connector to re-pin.
Two: Replacing the orange capacitor in the cabinet is easy and a must. It's also not a bad time to replace those bridge rectifiers for peace of mind.
Three: Grounding. There are a few different methods on how to do it and jump them. The method I used was to do each board individually, and all wires tied back to a nut and bolt off to the side of the backbox, and then back to the grounding plane in the bottom of the cabinet. It took very little time to do, and if I need to take a board out to service it, I simply undo the nut/bolt and it's out easy.
The reason for the grounding mod is because the connectors daisy chained the ground from the factory, and this can fail. By adding your ground mod, you're adding insurance. Doing the extra two wires at the cpu/driver harness is extra insurance, but not to be done as a stand alone mod. Doing all of it may be overkill, but it's also great peace of mind.
The harness from cpu/driver is another key piece. Inspect this/replace this/re-pin if necessary.
Some are a fan of the power supply, I am not. To me, they are more trouble then they're worth. More often than not, the bottom pins will need to be soldered due to cold solder/cracking. It's a slight pita, because you have to split the case to do it.
I go with the cheap rottendog board ($67) as I've never had a problem with them. Some of the rottendog boards are easy, plug and play replacements, but the original boards can be okay too. Same goes for the pop bumper drivers. It's best to update them or replace them (new ones are about $20 each) If you don't do either, you're bound to get a pop bumper failure sooner than later.
If you're sure on the above things, the game runs pretty damn good. There are several other fixes and mods to do along the way as well, but it's a pretty straight forward game overall once you learn the ins and outs.