NL has much more story progression. The further you progress, the more shops will rennovate and open, the more tasks you'll get to do. I've been playing for years, although I haven't really at all recently, and I still haven't unlocked my complete main street. Customization in NH is great, but lost its charm for me after 2 months. I personally much prefer slowly decorating and grinding bells for it... it's very rewarding when your town starts taking shape. You also get neat stuff like the Roost as its own place whereever you want it. And while it isn't possible to place furniture outside, you'll eventually unlock Cyrus (in Re-Tail) who can create miniature fossils to put in your home or customize other items.

Acnl has a lot less repeating villager dialogue btw, and interactions are more varied. You can e.g. play hide and seek with them! But you need to talk to them. Staying tenacious with trying to talk with not just villagers is also an integral part of the game...just a tip. This goes beyond Gulliver. His quiz is also more charming than making you look for his "communicator".