I bought books, phone case, enamel pins, acrylic standees, washi tapes, etc.
You can't really track your order with the free delivery option (i'm not sure if you can track your order if you pay the shipping fee). The delivery can be quite long, from 2 weeks to 2.5 months.
Some merchants sell their products at a very cheap price, but they don't offer free shipping and the shipping fee is ridiculously expensive. That's because they gain profit from the shipping fee instead.
There are a lot of counterfeit products. Even though Aliexpress says they prohibit counterfeit goods, they won't ban the sellers that sell counterfeits as long as the seller blatantly let you know that the goods they are selling are bootlegs (one look at the picture and you should know that it is a bootleg).
Once, i bought a counterfeit book without knowing it was a counterfeit because most of the reviews say that it is an original book. Can't blame them though, the book quality is good for a counterfeit. Later, i managed to get a refund from aliexpress after i filed a complaint and gave them my evidences (comparing the bootleg book and the original book).
Also, not everything here is cheap, so you have to know how much a product is worth actually. Don't be stupid.
In conclusion, if you have no problem with late delivery, counterfeit goods, and spending more time/effort in finding trusted sellers, then everything is good.