In order, from easiest to most difficult for me:
* Toys are fairly easy, especially following the extended review format.
* Lingerie I find easy as well, though it takes a little longer, as I like to take measurements of the actual item.
* BDSM products can be tricky. How do you describe how a paddle feels? So much of that depends on how sensitive you are and how your partner wields it. But in general, explaining the quality and construction of the toy isn't too difficult.
*Lubes are difficult - so subjective! Besides, now that I've found two lubes I really love and that don't irritate my skin, I'm not really interested in rocking the boat. I'd still like to finish reviewing the ones I already own though.
* I've only tried reviewing one dvd. I don't think I'll do that often. You think it would be easier, because non-porn movie reviews are all over the web to serve as examples. I think I dislike it because actually watching the dvd takes a lot longer than a session with a toy or trying on a piece of lingerie.