To clarify, my feelings towards Kafka are from the POV of someone who has had to build a managed service on top of it, which is not the common use case (for which many people seem to be happy with). Other people may have more positive experiences.

In my experience, Kafka is a solid system when you work in its wheelhouse, which is a relatively static set of servers / topics, that you add to slowly and deliberately. If you can't use something like Kinesis, then its a good choice.

In Kafka, programmatic administration is generally an afterthought. They have APIs for doing things, but they generally involve directly modifying znodes. Simple things don't work or have bugs, deleting topics didn't work at all until 0.8.2, and even now has bugs. We've seen cases where if you delete a topic while an ISR is shrinking or expanding, your cluster can get into an unrecoverable state where you have to reboot everything, and even then it doesn't always get fixed. Most of the time you are expected to use scripts to modify everything (there's a wide variety of systems out there that try to build mgmt on top of kafka).

Its dependency on Zookeeper is a pain, and limits scalability of topic / partition counts. Rebalancing topics will reset retention periods because they use the last modified ts of the segment files to check for oldness, meaning if you rebalance often, you need extra disk space laying around. ZK has some bugs with its DNS handling, which affects Kafka if you try and use DNS.

It has throttling, but its by client id, what you'd like in some cases, is to say that a node has X throughput, and have the broker be able to somewhat guarantee that throughput, and create backpressure when clients are overwhelming it. Otherwise your latency can go through the roof. You also want replication to play nice with client requests, and it doesn't (if you add a new broker and move a bunch of partitions to it, you'll light up all your other brokers while it replicates, and cause timeouts).

Its replication story can cause issues when network partitions come into play.

It's highly configurable like many Apache projects, which is a blessing and a curse, as your team has to know all the knobs, both consumer / producer / broker side.

The alternative if you are at a company with the resources to do so (mine is), is to build something that fits your use case better than Kafka, or to use a hosted service like this, or Kinesis.