I owned this game as a kid and personally really like Fester's Quest. The game difficulty at bosses is reduced a bit once you learn that any "family acquired" item is fully replenished after you defeat a boss, meaning you should be spamming potions, invisible potions, TNT, and missiles very liberally.
Still, it's hard to deny the game's many flaws. I wrote about them almost 10 years ago on the Fester's Quest board:
1. Gun design is horrendous given that it cannot pass through walls. This makes it impossible to hit enemies at times when going through tight passages. Also, the abundance of "circular" fire weapons that often miss enemies is annoying too. The game basically requires you to grind to level 8 at the beginning to get a decent weapon.
2. This game almost necessitates a turbo controller. Again, speaks to bad gun design.
3. When you die, you go back to the beginning. This just adds to annoyance more than challenge. You should be able to start at the point after the last boss you beat. You should also be able to back track after beating bosses (without having to do) in case you want to reclaim items.
4. The gun and whip downgrades. What the hell is the point of these? Nothing is more annoying that having the level 8 gun in the sewers and accidentally picking up the downgrade, making your weapon now useless. Same thing with the whip -- since the whip also picks up items, it's way too easy to accidentally pick up a downgrade while you're slashing enemies. Again, these add nothing but annoyance. I'd be fine if the the upgrades were less common if it meant no downgrades.
5. Poorly designed enemy re-spawn. This game really penalizes you for not moving forward constantly. Way too easy to get overwhelmed by enemies when you're just standing around or backtracking, and this is often the case when you have a weak gun or cannot shoot enemies.