Hi Ross,
to IIS.
The world of eyepieces is a vast one. Thing is eyepieces are designed to perform best in certain telescopes over others. The focus of a telescope is not a mere point, but a 'plain', and not a flat one either. Depending on the optical design of the scope this plain can actually be convex or concave in shape. How strongly convex or concave the shape is also varies, this time in relation to the focal ratio. There are some other lesser point too, but we'll leave these out for now (thank goodness for small mercies!
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Eyepieces in turn are actually designed to deal best with certain focal plain shapes than others. And as a result where one eyepiece is great in one scope design (and this is important), and can give a totally unusable image in another scope.
Eyepiece design has also followed closely and sometimes far behind telescope technology. New and exotic glass types have allowed newer designs to be developed, allowing for improved image quality with wider apparent fields of view, and much longer eye relief.
All this might seem complex, but really it isn't. It's like comparing a Ferrari F1 race car from 50 years ago to the current car - both go fast, but one much faster than the other and handles much better. But don't expect either to do well crossing over a sand dune. See what I mean?
Even within eyepiece 'types' there is a big difference. Plossl design is not a new one, and was designed for Newtonians, so it is no mistake they perform very well in Newt's. But, make the focal ratio of the Newt faster than f/6, and short falls start becoming apparent. Then, add to the mix that Plossl's ain't all the same, and this really becomes complex (yes, complex only now!). TeleVue plossls have been mentioned. These are not the same beast as the cheapies. And even in the cheapie range there is a difference. Doesn't mean you wouldn't be happy with cheapie plossls either as they are still better than some other eyepiece designs in certain scopes!
But, big $$$ is not the be all and end all. While big $$$ eyepieces are nice, very nice in some instances, they should not dictate your enjoyment, nor your visual preferences. It is a decision you should make on your own after trying out many different ones and reading as much as you can and asking questions.
I won't say which eyepiece to buy. I don't even know what scope you have to make offer an appropriate selection. What I will suggest is for you to get to a star party, formal club one or informal, with your scope, and look to borrow different eyepieces to see how they perform for YOUR eyes. Then you will best equipped to make an eyepiece choice for yourself.
Mental.