The plugin has great functionality, some of the best! But…

Akismet has been killing it with SPAM prevention for so very, very long. Everyone knows it rocks.

The only two complaints I have are:

1. There is a general lack of documentation when you want to integrate it into your own plugins and themes.
2. The billing / administrative side has had issues over the last few years. As they’ve moved to more aggressively make people pay for the service (I am a paid customer), even after upgrading to a paid version, errors and warnings would still appear in my clients’ sites – which of course is a reflection on me. Akismet / Automattic has been generally quick to resolve these, but I have had to write in multiple times to get this assistance.