Here are some that I can think of on the top of my head:
- It's volatility in price(currently). Hence holding your funds entirely on bitcoin is a huge risk despite the advantages.
- Very unsafe for careless and technologically-illiterate people. Logging in to a phishing link? Say goodbye to your exchange's funds. Forgot to list down your wallet's seed? Say goodbye to you wallet's funds.
- Unable to operate offline or non-electronically. This is a downside on more on the 3rd world countries, whereas most poor people can't even afford smartphones or any device that can hold bitcoin.
- Not-so-good transaction fees and time. Transaction fees and times are definitely alot better now compared to months ago, but I still remember the days when txs were almost instant, with very very low fees.
- My personal opinion: The name "bitcoin". I personally think it sounds like something a person involved in pyramid schemes and Ponzi scams would use.
I do want to take a toll from the points highlighted here and find them of real and greater relevance even to the adoption of Bitcoin as a digital currency. Part of the disadvantages are also found within its advantages; take a look at the idea of decentralization, this idea is like a somewhat threat to some government of a country not making them accept the change Cryptocurrency is bringing in. I do want to buttress on the transaction fee area which some friends have been lamenting about; this is with respect to different wallets though. I experienced a high transaction fee this morning; the transaction fee was higher ×7 of what I sent!