These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Harvest Moon 64
Base Breaker: Somewhat. Due to Flanderization and Character Exaggeration in future games related to these characters, also due to the series being Lighter and Softer recently, this game is often used to point out the others faults. It's considered the best HM game by most fans, so it's no surprise.
Karen likes dogs, so showings yours to her increases her affection. However, this isn't affected by the normal "one affection boost per day" rule, so you can get Karen from "doesn't know you from a hole in the ground" to "madly and passionately in love with you" on the first day.
The Betting Mini-Game at the horse and dog races allows you to cancel your bid (refunding your money) without actually cancelling the bet you made, allowing you to get the benefits of the bet without any of the risk.
One glitch made your dog disappear if you left him in your bathroom. He would still bark in response to you blowing the whistle in there, but he'd never show up. Sometimes referred to as "flushing your dog down the toilet".
Even Better Sequel: It's not the second game in the franchise, however it is the sequel to the original.
Sequel Displacement: HM64 is more known of than the original SNES Harvest Moon. However, the Playstation counterpart, Back to Nature, features many of the same characters (though with different relationships and somewhat different personalities) and is far better remembered than HM64. This is largely due to the fact the GBA game Friends of Mineral Town (which is essentially an enhanced port of Back to Nature) was the first Harvest Moon game played by a great deal of fans. HM64's version of the characters were basically ignored by Marvelous until Tree of Tranquility, when Gray and Elli are referenced to in their original roles.
Unfortunate Implications: Kai is an Ambiguously Brown man who works at a vineyard whom he doesn't own in an Eagleland-type environment. A few people have connected this to slavery, though Kai obviously is a free person and enjoys his work.