The most important aspect of any website is to facilitate the reader. Blogging has the additional factor of providing a two way conversation, so an easy to use site is essential.
I visit many blogs in the course of a day, and some of them make the very business of interaction so complicated that I tend not to revisit.
The most important aspect is to allow commenting to be as easy as possible. Blogger [the free service] is a nightmare in this respect as it involves popups and Captchas which I hate. In general, most blogs are easy to comment on, but they lack a couple of features which I think are rather irritating.
Another thing which I find irritating is to write a comment, submit it, and then find a glaring typo or omission when it is too late to do anything about it. A very simple solution to this one is to install ‘WP Ajax Edit Comments’. Unfortunately, I see they are about to start charging for updates to this, so I will either stick with my current version, or find an alternative. In the meantime, this allows the commenter a pre-set period of time to revisit and edit their comments.
One plug-in I like, though it is not essential is ‘MCEComments’. This embeds the TinyMCE code and adds the ability to format text in the comments, such as Bold or Italics. The plug-in can be fairly easily tweaked to provide a huge range of facilities such as justification, image embedding and link embedding. Most of these are best left off, but it is nice to have the facility if required.