Most interesting to me wasn't the browser itself, but the live demo (java required) that you can run. In it, you get a preview of exactly what Opera 4.0 Mini feels like, minus the fact you're using a mouse instead of a phone. If you're interested they have a large list of supported phones.
Opera Mini is arguably more functional than the micro IE built into Windows Mobile 5, though is not as robust as Opera Mobile. It lacks support for many things, such as offline browsing and opening local files. However, Mini is a free product and so at the very least worth a try.