Opera 3.51 was a bad disappointment. Also that browser had bad bugs. I though to put the whole application into the trash and newer download that application into my hard disk. Opera 5.11 is an excellent browser with fine CSS1 and quite fine CSS2 implementation. Because it is today available as ad-sponsored version, I hope that Opera 5.x could get much users.
Opera is quite standard-compliant.
All Opera browsers have however incorrect handling of nested frame sets . Opera is fast, handy and the security is at the top level . The newest version is quite reliable and fast. Even if Opera supports few proprietary features, Opera Software respects however highly web standards. If Opera could be more common browser, web standards could be more appreciated.