I personally really like what Monero is doing with blockchain, but in most cases attempts at cryptocurrency (when not outright scams) fail in terms of privacy or performance. Bitcoin (the most popular one) has both of these problems, it is slow, limited to just around 7 transactions per second. Bitcoin also lacks any privacy, with transaction history completely public. Monero has to do a whole lot of work to obfuscate transaction history.

Currently basically all of these have another scalability problem due to the size of the blockchain constantly getting bigger, with Monero's strething up to 150GB and growing.