You can't really beat a game like Animal Crossing as it doesn't have a proper ending credit sequence. However, you can beat it under the "100%" category as there is a goal to complete.
And for me, 100% means:
- Pay off all house loans completely.
- Unlock (and build) all permanent structures, including shops.
- Complete the Museum.
- Complete the Bug and Fish encyclopedia.
- Obtain all Silver and Gold tools.
- Obtain all Medals.
- Complete the Catalog.
- Obtain all villager and NPC pictures (they're a collectable item, even if not in catalog).
- Unlock all PWPs.
- Maximum Bells (999,999,999) in your ABD.
If you want a more reasonable "100%", remove "All Medals" and "All Villager/NPC Pictures".
For me "beating animal crossing" or more accurately as Khaelis said, 100% complete means the following:
-Having the town landscaped to my satisfaction
-Unlocked all shops and buildings
-Complete house with: complete exterior, full sized rooms, all storage and all loans paid off
-Unlocked all PWPs
-Obtain all gold tools
-Complete museum'
-Obtain all dream villagers
-A completed themed town that's organised into sections
-Lots of bells
-All medals
-Have citizen satification at 100%/perfect town
-Grow lots of hybrids and Jacobs ladders
Having full catalogs and villager pics isn't very important to me but that's just me. A lot of it is aesthetic to me
- completely fill up the museum
- have all of the gold tools
- complete the catalog
- have all of my dream villagers
- have my town look exactly how I want
- unlock all of the shops and the police station, coffee shop, etc.
- be best friends with at least half of my villagers
- fully expand my house
- have achieved perfect town status
- fill up the encyclopedias
- collect all of the badges
- museum filled
- all tools including the golden tools and the silver ones
- all badges
- all bugs, fishes, deep water animals.
- have all your villager's pictures obtained by being friends with them
-have perfect town status
- filled out catalog
- pay off all loans